ui: signal pages honour the signal lock and disable the plot a signal is already on

The per-signal page bypassed the signals lock for the acquire tick and the math
Edit/Delete buttons, and offered "Plot on r" for a plot the signal was already on.
A removed page also let another signal's page show during the close animation.

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

docs/claude/probe-readings.md

@@ -2637,12 +2637,15 @@ left the caller's `false` alone would read `dock_shown=0 default=1 ok=0`. The pr
 ## `[signalpage]`
 
 ```
-[signalpage] name=sine open=1 pages=1 enable_visible=1 plot_buttons=1 plot_on_row0=1 removed=1 btn_row0=1 back_to_list=1 row_opens=1 pruned=1 rows=1
+[signalpage] name=sine open=1 pages=1 enable_visible=1 plot_buttons=1 plot_on_row0=1 plot_on_row0_disabled=1 locked_enable_sensitive=0 removed=1 btn_row0=1 back_to_list=1 row_opens=1 pruned=1 rows=1
 ```
 
 `UDPSCOPE_PROBE_SIGNAL_PAGES_MS` builds and drives the page of the first streamed signal. `open=1` (the slide-over shows `signal:<name>`), `pages=1`
 (one page in `App::signal_pages`), `enable_visible=1` (the acquire tick is shown in live mode; `0` in a file view), `plot_buttons=` equal to
-`rows=` (one "Plot on" button per figure row), `plot_on_row0=1` (`assign_signal_to_row()` returned true and the signal is plotted), `removed=1`
+`rows=` (one "Plot on" button per figure row), `plot_on_row0=1` (`assign_signal_to_row()` returned true and the signal is plotted, from a state where the probe first took it off every plot), `plot_on_row0_disabled=1`
+(after the page refilled with the signal on plot 1, that plot's "Plot on" button is insensitive, "already on this plot"; `0` is a button that would put the signal in a second slot of
+the same plot), `locked_enable_sensitive=0` (with `signals_locked` set and `signal_pages_sync()` run, the page's Acquire/Compute tick is insensitive; `1` is a page that bypasses
+the signal lock -- the same goes for a math channel's Edit graph and Delete, which the probe does not read; the probe restores the lock), `removed=1`
 (the page's "Remove from plots" took it off), `btn_row0=1` (the "Plot on 1" button, the user's path, put it back), `back_to_list=1` ("All signals"
 target), `row_opens=1` (activating the list row opens the page), and `pruned=1`: a math channel's page was opened, its **Delete** button clicked, and
 the slide-over closed and the page was dropped by `signal_pages_sync()`. `pruned=-1` means no math channel could be added; `0` is a stale page.