ui: the trigger's wave is a full period again

The bold pass had turned the trigger into half a period — a signal rising above its level — and that
lost the thing the glyph is for: the crossings. A crest and a trough read as a wave; a hump reads as a
hill, and a trigger that shows no crossing names the "above the level" half of an event. The full-period
sine with the dashed level through it is restored, exactly as it was, and the Signals pill carries the
same wave again so the pill and the toolbar button stay one picture.

The Measure glyph keeps the bold redesign, which is the part that was better: two cursors (a cap over two
4px dashes) beside a ruler of two bands with three 2x4 marks and no end caps. The Signals pill also keeps
its two bold channel rows.

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 12352 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
-**11774** against C99's 4095-byte string-literal limit with the seven action icons and the two app icons
+**12352** 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`