docs: the sample budget in samples per signal, the memory limit and the planner probe lines

Converts every --buffer-mb / buffer_mb mention to --buffer-samples / buffer_samples,
records the unit change as a deviation (README, SPECS, CLAUDE.md), documents the
buffer: and planner: dump lines and the new Preferences row, and updates the help
pages and the help-shot script.

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

help/C/org.udpscope.app/trigger.page

@@ -117,7 +117,7 @@
       layout the app starts with — has room for one older acquisition of each of them; a row per
       signal has room for all seven.</p></item>
       <item><p><em>Memory.</em> A retained acquisition is a whole window copied out of the ring,
-      so persistence may hold at most as much again as the buffer (<gui>--buffer-mb</gui>) does.
+      so persistence may hold at most as much again as the buffer takes (see <cmd>--buffer-samples</cmd> and <cmd>--memory-limit-mb</cmd>).
       On a long window at a high sample rate that bound is reached before the eighth layer.</p></item>
     </list>
   <section id="persistence">