ui: per-signal slide-over pages; the drop's assignment and the colour reset as shared functions

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

docs/claude/verification.md

@@ -447,6 +447,10 @@ precedent, not an exception.
   read `click_inside_closes=0 still_open=1 click_outside_closes=1 esc_closes=1 closed=1`. For a screenshot
   add `UDPSCOPE_PROBE_SLIDEOVER_HOLD=1`, which leaves the page open after line 1 (run with `GSK_RENDERER=cairo`
   and `import -window root`): the panel must be drawn over the traces, opaque.
+- `UDPSCOPE_PROBE_SIGNAL_PAGES_MS=1500` with `UDPSCOPE_EXIT_AFTER_MS=5000` and `UDPSCOPE_ENABLE_ALL_MS=500` -- the
+  per-signal `signal:<name>` slide-over pages. **Against a config that has already seen the tour** (a first run's
+  auto-tour closes the slide-over at about 1.5 s, which is when this probe opens its page). One `[signalpage]` line;
+  see [probe-readings.md](probe-readings.md).
 - `UDPSCOPE_PROBE_BADGES_MS=2000` with `UDPSCOPE_EXIT_AFTER_MS=5000` and `UDPSCOPE_ENABLE_ALL_MS=500` -- the badge
   bar under the plot. One `[badges]` line, which must read `table_bad=0 fixed=1 open_marked=1 page_open=1
   closed_unmarked=1`: `table_bad` counts the rows of the 16-input `trigger_badge_state()` table the probe