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/source.page

@@ -28,7 +28,7 @@
         stored <em>configuration</em> (<code>host:port · name</code>, its note, and the
         settings it carries), newest first, plus a <gui>New host…</gui> form that takes the
         address <em>and</em> the configuration it belongs to — its name and note, the
-        <gui>buffer size</gui>, and whether time is relative or absolute. A row's pencil
+        <gui>samples per signal</gui>, and whether time is relative or absolute. A row's pencil
         button opens the same form on that configuration, pre-filled, and changes to its name
         or address move it (the old file is deleted).</p>
       </item>