ui: sidebar tab selector uses text labels instead of icons

The two drawn tab glyphs were judged not understandable enough; the
switcher goes to the wide policy with titles only, and the glyphs,
their gresource entries and the icon-naming code are removed.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

docs/claude/invariants-gtk-and-chrome.md

@@ -51,38 +51,20 @@ Part of [CLAUDE.md](../../CLAUDE.md). These are rules that cost a defect to lear
   how the first version of that line earned them. What stays in the menu is what acts on the *data*
   (Fit, Export, Configurations) and the one editor that is not a pane (the layout editor): the signal list
   is a *tab* of the sidebar, so there is nothing left to reveal or hide about it. The Arm/Disarm button in the trigger panel still has text.
-- **Seven of this app's icons are its own, and they are a `GResource` compiled into the
+- **Five of this app's icons are its own, and they are a `GResource` compiled into the
   binary.** No icon theme has a glyph for an oscilloscope trigger, a pair of cursors or a
   measurement ruler, and the stock names those buttons used to carry said something else
   entirely: a *record dot* for the trigger and three different **magnifiers** for cursors,
-  measurements and math. `src/icons/scalable/actions/udpscope-{trigger,cursors,measure,events,resize-rows,tab-measure,tab-signals}-symbolic.svg`
-  are the seven action icons. `udpscope-math-symbolic` left with the toolbar toggle that was its last
+  measurements and math. `src/icons/scalable/actions/udpscope-{trigger,cursors,measure,events,resize-rows}-symbolic.svg`
+  are the five action icons. `udpscope-math-symbolic` left with the toolbar toggle that was its last
   user; `udpscope-measure-symbolic` **stayed**, because the Preferences window's Plot page carries it --
   an icon with a live user is not an orphan, whatever the toggle that introduced it did -- and it is
-  the Preferences window's icon, not the tab's.
+  the Preferences window's icon.
 
-  The two **tabs** got glyphs of their own, and each is a *pair* rather than one of the icons above.
-  `udpscope-tab-measure-symbolic` is two cursors beside the ruler they read against — each a cap over two
-  bold dashes, beside a ruler of two bands with three marks between them and **no end caps** (a closed
-  frame reads as a rectangle, and costs a fifth of the ink on two lines that say nothing) — and
-  `udpscope-tab-signals-symbolic` is a sine crossing its dashed level, beside two bold channel rows. They
-  are not reuses, because a glyph the toolbar already carries means two things the moment a tab shows it
-  too; instead the *trigger's* own icon (`udpscope-trigger-symbolic`) was redrawn to the Signals pill's
-  picture, so the pill and the button that turns the trigger on are recognisably about the same thing.
-  The wave is a **full period and not a hump**: a crest and a trough are what make it read as a wave
-  rather than as a hill, and the level's dashes survive between the crossings. (A hump was tried and
-  reverted — it named the "above the level" half of a trigger and lost the crossings, which is the half
-  that matters.)
-  Both are **32x16** composites drawn **bold** — one thick band, two thick dashes, few features — because
-  at this size a thin wave or a 1px tick reads as *texture* rather than as a shape, which is what "not
-  clear" looks like. Wider than tall on purpose: a 16px square cell carries one motif, not a pair. And
-  **GDK paints an icon into a square box whatever the document's aspect** (measured:
-  `gtk_icon_theme_lookup_icon()` at 32 reports `32x32`, and librsvg fits it to `32x16`), so the pair is
-  letterboxed rather than stretched — and the pill's image is given `pixel_size` 32 in `name_side_tabs()`,
-  which draws the artwork at the size it is written, so its bars stay crisp. Every glyph here is
-  **inset two pixels**, because art flush with the cell edge is what a button's padding or a crop takes a
-  pixel off, and a fractional scale is what would blur it, which is why nothing is drawn at 24 or 48. The
-  two tab glyphs measure 29% and 30% ink, inside the range the icons above them set.
+  The sidebar's **tabs have no icons any more**: two glyphs (`udpscope-tab-measure-symbolic`,
+  `udpscope-tab-signals-symbolic`, each a 32x16 pair) were drawn for them and judged not understandable
+  enough, so the tabs are text and both SVGs were deleted. The *trigger's* own icon was redrawn to the
+  Signals glyph's picture at that time and kept it.
 - **A shortcut table row's `accel` is GTK accelerator syntax, and a pointer gesture has
   none.** `src/shortcuts.cpp`'s strings are handed to `AdwShortcutsItem`, which parses them
   with `gtk_accelerator_parse()` — so they are `"space"`, `"<Control>e"`, `"<Control>slash"`,
@@ -264,16 +246,13 @@ Part of [CLAUDE.md](../../CLAUDE.md). These are rules that cost a defect to lear
   allocation read in the sidebar is a debug capture, and each reads 0 on the page that is *not*
   current -- a change in what the reading means, not a defect, and no functional code may depend on
   those numbers.
-- **`AdwViewSwitcherPolicy.narrow` still draws a label; an *empty title* is what makes a pill an icon.**
-  Measured on libadwaita 1.10: with `narrow` and a title, the pill holds a `GtkImage` **and** a
-  `GtkLabel` — 48px of "Measure" inside a 54px pill — so the policy alone does not give an icon-only tab
-  bar. The sidebar's pages therefore have **no title** (their `name` is what identifies them to
-  `select_side_tab()` and the session file) and the pills are *named in code* instead: the first tick
-  calls `name_side_tabs()`, which walks the switcher's children — the pills are there in page order, and
-  `AdwViewSwitcherButton` is not a public type, so there is no type check to make — and sets each pill's
-  **tooltip and accessible name** from the page's name, then hides the empty label that would otherwise
-  leave the icon off-centre. An icon-only pill is still a named control for a screen reader, and
-  `switcher: … pills=2 labels=0 names=2` is the reading for all three facts at once.
+- **The sidebar's tabs are text: `AdwViewSwitcherPolicy.wide`, a title on every page, no icon.** The
+  built-in pages get their titles in the `.ui` and a source kind's pages from `SourcePanel::title`
+  (`adw_view_stack_add_titled`); the page's *name* still identifies it to `select_side_tab()` and the
+  session file. An icon-only version existed (policy `narrow`, empty titles, the pills named in code by
+  `name_side_tabs()`, because `narrow` still draws a label beside an icon); it was reversed because the
+  glyphs were not understandable. A page added with an empty title is a blank pill, and
+  `switcher: … pills=N labels=N pages=N` reads it as `labels` below `pills`.
 - **An *overlaid* sidebar covers the plot, so a drag out of it has nowhere to land.** `collapsed` in an
   `AdwOverlaySplitView` means the sidebar sits *on* the plot rather than beside it: the pointer is over the
   list, never over a drop target, and a signal can be dragged but not dropped. `row_drag_sidebar()` hides