feat(kb-gates): one work log per bundle, and the quarantine is not bundle content

The bundle had two work logs. `core/log.md` was created "for tracking core directory
modifications" and holds two entries of pure migration bookkeeping (file moved,
directory created, log created) — every one recoverable from `git log` — plus a date
for the OKF conversion (2026-07-15) that matches neither the bundle log (2026-01-15)
nor git history, where the OKF rebuild lands 2026-08-28. `core/index.md` was still
linking it, which is exactly how a stale page stays in circulation. kb-lint now reports
any `log.md` that is not the bundle root's; the page moved to omp-docs/core/.AGENTTRASH/
per the trash convention, and the core index points one level up.

Both gates also walked `.AGENTTRASH/`, so trashing a page turned them red: kb-lint
demanded frontmatter from a quarantined page and kb-coverage demanded an index for the
trash directory. A gate that only goes green once the quarantined copy is deleted is a
gate that deletes history, so both skip any path containing `.AGENTTRASH` — pinned by a
test in each suite, and kb-coverage finally gets its own test file.

omp-docs/core/index.md

@@ -16,6 +16,4 @@ These files define the structural conventions that govern the agent system itsel
 * [OMP Status Line Customization](statusline.md) — How presets, composer shapes, and segment arrays actually interact; the fleet's tuned bar. (moved from /pi/, 2026-10-19)
 * [OMP Subagent Limits & Fan-out Policy](subagent-limits.md) — Live caps: concurrency 2, no nested spawns (the `maxRecursionDepth: 0` trap), per-endpoint in-flight ceilings, isolation policy. (moved from /pi/, 2026-10-19)
 
-## Change Tracking
-
-* [Bundle Change Log](log.md) — Chronological update history.
+**Change log:** the bundle keeps exactly one, one level up — [Bundle Change Log](../log.md). A directory here never has its own.