ui: bolder tab glyphs, and the trigger shares the Signals pill's picture

The previous pair were detailed miniatures — 1px ticks, 2px dashes, a 13-column wave — and at 32x16 that
reads as *texture* rather than as a shape, which is what "not clear" looks like. All three glyphs are
redrawn bold: one thick band, two thick dashes, few features.

- **Measure** is two cursors beside the ruler they read against. Each cursor is a cap over two bold
  dashes (4px), where three 2px dashes read as a dotted column; the ruler is two bands with three 2x4
  marks between them and **no end caps**, because a closed frame reads as a rectangle and costs a fifth
  of the ink on two lines that say nothing. This is the layout whose first attempt looked like two icons
  in a box — the difference is entirely the weight and the open ends.
- **Signals** is a signal rising above its level beside two bold channel rows. Half a period instead of
  a full one: at this size a full period is a zigzag and a hump is unmistakably a wave, and the level's
  marks survive on both sides of it instead of being swallowed by the crest.
- **The trigger's own icon** is now the same picture as the Signals pill, so the pill and the button that
  turns the trigger on are recognisably about the same thing.

Each was rendered and read back as an ink map at 1:1 and at 2x before it was installed, and three
candidates were compared for the Measure glyph (markers *on* a scale, cursors *over* a ruler, and this):
the first two turned the marks and the shafts into blobs at the crossings. Ink is 18%, 30% and 29%,
inside the range the icons above them set, and everything stays inset two pixels.

Verified: `toolbar icons: trigger=udpscope-trigger-symbolic(ok)`;
`page icons: measure=udpscope-tab-measure-symbolic(ok) signals=udpscope-tab-signals-symbolic(ok)`;
`switcher: policy=narrow pills=2 labels=0 names=2 icon=32x32 size=308x36`; `[side-tab-probe] … advanced=4`;
the Preferences dialog opened in the same run with no "not present"; `make test-ui` 14 files; zero
`Gtk-CRITICAL`. The icons' blob is 11774 bytes, still over the C99 limit, so the clean-build warning
count stays four.

src/icons/scalable/actions/udpscope-tab-measure-symbolic.svg

@@ -1,26 +1,21 @@
 <?xml version="1.0" encoding="UTF-8"?>
 <!-- SPDX-License-Identifier: MIT -->
 <!-- SPDX-FileCopyrightText: 2026 Martino Ferrari -->
-<!-- The Measure tab: two cursors standing on the scale they read against. The scale is one band with
-     alternating marks rather than the closed ruler body `udpscope-measure-symbolic` draws for the
-     Preferences window: at 32x16 a frame costs a fifth of the ink on two lines that say nothing, and
-     the cursors are what this tab is *for*. Each marker is centred on one of the marks — a cap over a
-     dashed shaft that meets the scale instead of hovering over it — so the two read as one instrument
-     rather than as two icons sharing a box. Both use the 2px weight of every other icon here, and
-     everything is inset two pixels, because art flush with the cell edge is what a button or a crop
-     clips. -->
+<!-- The Measure tab: two cursors beside the ruler they read against. Each cursor is a cap over two
+     bold dashes — the mark the toolbar's cursors button carries, at a weight that survives this size.
+     The ruler is two bands with three marks between them and *no end caps*: a closed frame reads as a
+     rectangle, and it costs a fifth of the ink on two lines that say nothing. Both motifs are centred
+     on the same line and share one weight, and everything is inset two pixels. -->
 <svg height="16px" width="32px" viewBox="0 0 32 16" xmlns="http://www.w3.org/2000/svg">
-  <path fill="#2e3436" d="M2 12 H30 V14 H2 Z
-                          M5 9 H7 V12 H5 Z
-                          M9 10 H11 V12 H9 Z
-                          M13 9 H15 V12 H13 Z
-                          M17 10 H19 V12 H17 Z
-                          M21 9 H23 V12 H21 Z
-                          M25 10 H27 V12 H25 Z
-                          M7 3 H12 V6 H7 Z
-                          M8 7 H11 V10 H8 Z
-                          M8 10 H11 V12 H8 Z
-                          M19 3 H24 V6 H19 Z
-                          M20 7 H23 V10 H20 Z
-                          M20 10 H23 V12 H20 Z"/>
+  <path fill="#2e3436" d="M2 2 H7 V5 H2 Z
+                          M3 6 H6 V10 H3 Z
+                          M3 11 H6 V14 H3 Z
+                          M9 2 H14 V5 H9 Z
+                          M10 6 H13 V10 H10 Z
+                          M10 11 H13 V14 H10 Z
+                          M17 4 H30 V6 H17 Z
+                          M17 10 H30 V12 H17 Z
+                          M18 6 H20 V10 H18 Z
+                          M22 6 H24 V10 H22 Z
+                          M26 6 H28 V10 H26 Z"/>
 </svg>

src/icons/scalable/actions/udpscope-tab-signals-symbolic.svg

@@ -1,32 +1,27 @@
 <?xml version="1.0" encoding="UTF-8"?>
 <!-- SPDX-License-Identifier: MIT -->
 <!-- SPDX-FileCopyrightText: 2026 Martino Ferrari -->
-<!-- The Signals tab: the toolbar's trigger picture — a sine with a dashed level through it — beside
-     the channel list. Sharing that picture is the point: the pill and the toolbar button that turns
-     the trigger on should be recognisably about the same thing. Three channel rows on the right, on
-     the left half's centre line, and everything inset two pixels, because art flush with the cell
-     edge is what a button or a crop clips. -->
+<!-- The Signals tab: the toolbar's trigger picture — a signal above its level — beside the channel
+     list. Sharing that picture is the point: the pill and the button that turns the trigger on should
+     be recognisably about the same thing. Two channel rows on the right, drawn bold for the same
+     reason the wave is, and everything inset two pixels. -->
 <svg height="16px" width="32px" viewBox="0 0 32 16" xmlns="http://www.w3.org/2000/svg">
-  <path fill="#2e3436" d="M2 6 H3 V10 H2 Z
-                          M3 4 H4 V8 H3 Z
-                          M4 3 H5 V7 H4 Z
-                          M5 2 H6 V6 H5 Z
-                          M6 3 H7 V7 H6 Z
-                          M7 4 H8 V8 H7 Z
-                          M8 6 H9 V10 H8 Z
-                          M9 8 H10 V12 H9 Z
-                          M10 9 H11 V13 H10 Z
-                          M11 10 H12 V14 H11 Z
-                          M12 9 H13 V13 H12 Z
-                          M13 8 H14 V12 H13 Z
-                          M14 6 H15 V10 H14 Z
-                          M2 7 H5 V9 H2 Z
-                          M7 7 H10 V9 H7 Z
-                          M12 7 H15 V9 H12 Z
-                          M18 2 H21 V5 H18 Z
-                          M23 3 H30 V5 H23 Z
-                          M18 7 H21 V10 H18 Z
-                          M23 8 H30 V10 H23 Z
-                          M18 12 H21 V15 H18 Z
-                          M23 13 H30 V15 H23 Z"/>
+  <path fill="#2e3436" d="M3 7 H4 V12 H3 Z
+                          M4 6 H5 V11 H4 Z
+                          M5 4 H6 V9 H5 Z
+                          M6 3 H7 V8 H6 Z
+                          M7 2 H8 V7 H7 Z
+                          M8 2 H9 V7 H8 Z
+                          M9 2 H10 V7 H9 Z
+                          M10 2 H11 V7 H10 Z
+                          M11 3 H12 V8 H11 Z
+                          M12 4 H13 V9 H12 Z
+                          M13 6 H14 V11 H13 Z
+                          M14 7 H15 V12 H14 Z
+                          M2 8 H3 V10 H2 Z
+                          M15 8 H17 V10 H15 Z
+                          M18 3 H23 V8 H18 Z
+                          M24 4 H30 V7 H24 Z
+                          M18 10 H23 V15 H18 Z
+                          M24 11 H30 V14 H24 Z"/>
 </svg>

src/icons/scalable/actions/udpscope-trigger-symbolic.svg

@@ -1,26 +1,22 @@
 <?xml version="1.0" encoding="UTF-8"?>
 <!-- SPDX-License-Identifier: MIT -->
 <!-- SPDX-FileCopyrightText: 2026 Martino Ferrari -->
-<!-- The trigger: a sine and the dashed level it is looked for at, which is what a trigger *is* on a
-     waveform that is not a step. It used to be a rising edge, and one edge names only one of the four
-     shape triggers the panel offers — a wave crossing a level names the trigger's job instead. One
-     period, one-pixel stairs, the way the plot rasterises its own traces, with the level through the
-     centre so the crest and the trough stand clear and the crossings fall on the steep parts. Inset
-     two pixels, like the tabs' glyphs, so no art is flush with an edge a button might clip. -->
+<!-- The trigger: a signal rising above the level it is looked for at, with the level showing on both
+     sides of it. One event, which is what the trigger is for. Bold on purpose: at this size a
+     thinner wave reads as texture, and the level has to survive as two clear marks rather than as a
+     dotted line. Inset two pixels like the tabs' glyphs, so no art sits flush with an edge a button
+     might clip. Whole-pixel stairs, the way the plot rasterises its own traces. -->
 <svg height="16px" width="16px" viewBox="0 0 16 16" xmlns="http://www.w3.org/2000/svg">
-  <path fill="#2e3436" d="M2 7 H3 V10 H2 Z
-                          M3 5 H4 V8 H3 Z
-                          M4 3 H5 V6 H4 Z
-                          M5 3 H6 V6 H5 Z
-                          M6 4 H7 V7 H6 Z
-                          M7 6 H8 V9 H7 Z
-                          M8 8 H9 V11 H8 Z
-                          M9 10 H10 V13 H9 Z
-                          M10 11 H11 V14 H10 Z
-                          M11 11 H12 V14 H11 Z
-                          M12 9 H13 V12 H12 Z
-                          M13 7 H14 V10 H13 Z
-                          M2 7 H5 V9 H2 Z
-                          M7 7 H10 V9 H7 Z
-                          M11 7 H14 V9 H11 Z"/>
+  <path fill="#2e3436" d="M3 7 H4 V11 H3 Z
+                          M4 5 H5 V9 H4 Z
+                          M5 4 H6 V8 H5 Z
+                          M6 3 H7 V7 H6 Z
+                          M7 2 H8 V6 H7 Z
+                          M8 2 H9 V6 H8 Z
+                          M9 3 H10 V7 H9 Z
+                          M10 4 H11 V8 H10 Z
+                          M11 5 H12 V9 H11 Z
+                          M12 7 H13 V11 H12 Z
+                          M2 8 H3 V10 H2 Z
+                          M13 8 H15 V10 H13 Z"/>
 </svg>