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-trigger-and-pinning.md

@@ -356,7 +356,7 @@ Part of [CLAUDE.md](../../CLAUDE.md). These are rules that cost a defect to lear
   `snapshot_bytes()` is the honest cost of one -- both stamp arrays, every channel's `f32` samples
   and the LOD pyramids built for them, i.e. ~4.5 bytes per sample per channel plus 8 per sample of
   clock -- and `prune_persist_locked()` cuts the set to **both** bounds: the depth, and
-  `persist_budget_bytes()`, which is the ring's own `--buffer-mb`, because persistence is a copy
+  `persist_budget_bytes()`, which is the planned ring bytes (`Partition::bytes()`), because persistence is a copy
   *of* what the rings hold and holding as much again is the honest ceiling for a display of it.
   `kMaxPersistDepth` is 8 for the different reason the panel needs one: the layer there is already
   invisible (0.8 %) and seven is all the free slots a one-signal row has. The depth is not the only