feat(collab): local-ops-only undo — remote applies skip the undo stack (ysync miss 09)

Ctrl+Z after a peer's edit no longer reverts (and re-broadcasts) the
peer's work, and the adopt undo-bomb is gone:

- doApply/doApplyItems (both editors) Push with SKIP_UNDO; the emit path
  is unaffected (suppression keys off s_applyingRemote, not undo).
- With SKIP_UNDO no picker owns removed items — the bindings free them
  after Push (explicit removals + upsert's remove-before-re-add; fields
  excluded: CHT_REMOVE hides them, parent keeps ownership). Freeing stays
  out of the fork commit classes so DRC's SKIP_UNDO callers can't
  double-free.
- Test hooks kicadCollabTestUndo/UndoDepth, registered per-editor AND in
  the kicad_editor dispatcher (merged image compiles out per-app
  registrations).
- kicad pointer: eeschema UUID undo guard + SKIP_UNDO connectivity split
  + quiet stale-entry drop (ca8877324c).
- tests/kicad/collab-undo.spec.ts: 5 scenarios (no undo entry from remote
  applies; selective undo; stranded replaced/deleted entries) — 5/5, plus
  collab/ysync regression 30 pass.
- docs: ysync-review 20 fix record; 09 marked FIXED; overview indexed.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_019ejJEvS7ogef2o9gVTXjmp

docs/features/ysync-review/00-overview.md

@@ -95,3 +95,4 @@ sending half emits NOTHING, not the bare removal the doc predicted).
 | 17 | [17-fixes-bugs-01-07.md](17-fixes-bugs-01-07.md) | Bugs 01–07 fixed & verified (2026-07-03); findings F5–F6; remaining follow-ups |
 | 18 | [18-miss08-opts-12-13.md](18-miss08-opts-12-13.md) | Miss 08 (lib_symbols + layout save-sync) + opts 12/13 implemented; opt 14 deferred (2026-07-03) |
 | 19 | [19-undo-option1-feasibility.md](19-undo-option1-feasibility.md) | Miss-09 option 1 (local-ops-only undo) feasibility research (2026-07-07): ~3–5 days, eeschema UUID-guard port is the core |
+| 20 | [20-fix-miss09-collab-aware-undo.md](20-fix-miss09-collab-aware-undo.md) | Miss 09 FIXED (2026-07-07): SKIP_UNDO remote applies + eeschema UUID guard + binding-owned removed-item lifetime; 5/5 e2e |