RLCR: BitLesson knowledge base rots silently — add a staleness/reference check + a `deprecate` action

[LukeLIN-web]

Summary

RLCR's BitLesson knowledge base (.humanize/bitlesson.md) is effectively append-only.
The round stop-gate validates the format of the ## BitLesson Delta (per docs/bitlesson.md:
Action ∈ none|add|update, IDs must exist), but nothing validates that existing lessons
are still accurate against the current repo. As the codebase refactors, lessons rot —
and a rotted lesson handed to an implementer by bitlesson-select.sh is worse than no
lesson, because it actively misleads.

Where it breaks (observed in a real knowledge base after one dir reorg)

A subsystem's code moved eval_audio_cot/scripts/ → scripts/audio_cot/ (output
namespace stayed outputs/eval_audio_cot/). All of the following passed the format-only gate:

• 3 lessons' Scope: lines still point at the old eval_audio_cot/scripts path (dir gone).
• A Solution: snippet says derive root via Path(__file__).resolve().parent.parent,
  but the file is now nested one level deeper, so current code uses parent.parent.parent
  — copying the lesson literally is off-by-one.
• A canonical path outputs/analysis/{score,go_nogo_decision}.json moved to
  outputs/eval_audio_cot/analysis/....
• Update (round 9) notes superseded by Update (round 22) linger with no way to retire them.

Root cause

• The Delta contract has no deprecate/delete action (only none|add|update), so
  superseded lessons and stale Update (round N) notes can only be piled on, never retired.
• No step ever re-checks that a lesson's cited paths / file:line refs / code snippets
  still resolve. (Cf. the agent-memory rule: "a memory naming a file is a claim it existed
  when written — verify before acting." BitLessons make the same claims but are never re-verified.)

Proposed improvements

1. Add deprecate (and/or delete) to the BitLesson Delta (Action: none|add|update|deprecate),
   with provenance ("superseded by BL-… / dir reorg"). Lets the loop retire dead lessons
   and consolidate old Updates.
2. A reference-resolution / staleness check — companion to bitlesson-select.sh, run at
   loop start or as a periodic gate — that parses each lesson's Scope paths + file:line
   refs and reports entries whose references no longer exist. Advisory by default; optionally
   blocking via a flag (like the existing --require-bitlesson-entry-for-none).
3. Selector surfaces staleness at point of use: when a lesson is selected, re-validate its
   referenced paths; if any don't resolve, tag it "possibly stale — verify before applying".
4. Update-note curation: when an entry accrues many Update (round N) lines, prompt to fold
   them into the Solution and drop superseded ones.

Scope / non-goals

Lesson content (the bug→fix knowledge) usually stays valid across refactors; only its
references drift. Default should be fix/flag references, not delete whole lessons —
deletion reserved for genuinely obsolete subsystems via the explicit deprecate action.

[LukeLIN-web]

propose a PR at #188