PR #23 (fork rebase) + upstream PR Martian-Engineering#530 review threads from coderabbit
+ copilot. Each fix is verified by a test where applicable; commit can
be cherry-picked safely on top of ea85941.

Fork PR #23 (18 threads, all REAL):
- Untrack node_modules symlink (machine-specific /Volumes/LEXAR path).
- changeset MD041: prefix first body line with H1.
- src/db/config.ts: route LCM_OBSERVED_WORK_MAINTENANCE_ENABLED through
  toBool() so invalid values fall through to plugin config rather than
  silently disabling the feature.
- src/db/migration.ts: add lcm_task_bridge_suggestions index aligned with
  listSuggestions ORDER BY (updated_at DESC, created_at DESC).
- src/engine.ts: getObservedWorkStore + getEventObservationStore now
  call ensureMigrated() — lcm_work_density / lcm_event_search reach
  the stores via these getters and must not bypass schema setup.
- src/store/sql-utils.ts (new) + observed-work-store + event-observation-store:
  extract duplicated placeholders() helper.
- src/store/task-bridge-suggestion-store.ts:
  * Replace task_id COALESCE with bare excluded.task_id on pending refresh
    so a kind change to create_task no longer leaves stale task references.
  * reviewSuggestion now trim()s suggestionId, mirroring upsertSuggestion.
  * datetime('now') -> strftime('%Y-%m-%dT%H:%M:%fZ', 'now') for ms
    precision so same-second writes get deterministic recency ordering.
- src/observed-work-extractor.ts:
  * findActiveItemsByTopic only runs when work.completed/possiblyResolves
    (eliminates O(N) per-line query on dense summaries).
  * classifyEvent now always runs even when the line was consumed as an
    active-work transition (Merged PR #X both resolves AND emits an event).
  * Skip a transition when transition.observedAt < activeItem.lastSeenAt
    so backfilled summaries can't close newer in-flight items.
- src/tools/lcm-work-density-tool.ts:
  * Resolve period bounds against deps.clock.now() (was new Date()).
  * Prefer per-conversation timezone via RollupStore.getTimezone, falling
    back to lcm.timezone (mirrors lcm_recent's read-side contract).
- src/store/observed-work-store.ts: ObservedWorkDensityQuery.now (ISO)
  threads the caller's clock through to getStaleRows so staleAfterDays
  cutoffs are deterministic under replay/frozen-clock tests.
- specs/lcm-observed-work-density-option-b.md: bring "implementation
  scaffold" + "not implemented yet" sections in line with shipped code
  (extraction is wired into maintain() in this branch).

Upstream PR Martian-Engineering#530 (1 thread):
- src/store/event-observation-store.ts: normalizeQueryKey now extracts
  PR numbers from URL forms ("...Martian-Engineering/pull/123", "Martian-Engineering/pull/123") so query by
  URL matches the canonical pr-N key.

Tests: 1009 pass (was 1004; +5 new regression tests).
Build: pass.