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>

docs/claude/invariants-math-channels.md

@@ -334,7 +334,7 @@ the assertion: `finite` must be about `M` minus the hole share, and `finite=0` b
   before the ring first wraps** (`base == 0`, where the two numberings coincide), which is why it reads
   as intermittent and uptime-dependent. The dump's `math '<name>': N samples vs M time slots` is the
   reading -- both numbers are `produced()`, so a mismatch *is* this defect -- but only on a run whose
-  ring has wrapped: give it a small `--buffer-mb`. `UDPSCOPE_PROBE_MATHWRAP_MS` is the probe that
+  ring has wrapped: give it a small `--buffer-samples`. `UDPSCOPE_PROBE_MATHWRAP_MS` is the probe that
   arranges exactly that, and it exists because **`math_probe` structurally cannot** reach this state:
   every edit that probe makes follows a structural change, which replans the buffer and restarts every
   ring at absolute 0, where both halves of this are identities.