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.

docs/claude/verification.md

@@ -16,7 +16,7 @@ xvfb-run -a env UDPSCOPE_EXIT_AFTER_MS=8000 UDPSCOPE_ENABLE_ALL_MS=1000 \
 Two baselines every run is read against. A clean build emits **four** warnings and no more: two
 `-Wmissing-field-initializers` on `MathNode::source` and `-Woverlength-strings` on **both**
 generated GResource `.c` files — the help pages' (**514660** bytes) and the icons', whose blob is
-**12624** against C99's 4095-byte string-literal limit with the seven action icons and the two app icons
+**11774** against C99's 4095-byte string-literal limit with the seven action icons and the two app icons
 that remain (a note about a generated file, which GCC itself supports) -- re-measured when
 the tab work changed the set (that icon left, the two tab glyphs arrived, and this file's
 help page was rewritten), which did not move the count; re-measure by touching each `*.gresource.xml`