fix: orphan accepted commit marker self-healing — auto-clear stale marker when no recoverable graph source exists

- Add maybeResolveOrphanAcceptedCommitMarker() for conservative orphan detection:
  - Chat-state sidecar rescue first (preserves marker, keeps mismatch diagnostic)
  - Only clears marker when ALL local sources confirmed absent
  - Guards: shadow-available, migration-failed, chat-switched all block clearing
- Enhance clearCurrentChatCommitMarker() with resetAcceptedRevision option
  - Resets lastAcceptedRevision and acceptedStorageTier when marker is orphan
- Integrate orphan resolution into loadGraphFromIndexedDb() empty+mismatch branch
- Update onDeleteCurrentIdbController/onDeleteAllIdbController to resetAcceptedRevision
- Update graph-persistence regressions:
  - Orphan marker scenario now auto-heals to EMPTY_CONFIRMED (was: permanently BLOCKED)
  - Add chat-state rescue guard test: sidecar data prevents marker clearing

ui/ui-actions-controller.js

@@ -1196,6 +1196,7 @@ export async function onDeleteCurrentIdbController(runtime) {
     runtime.clearCurrentChatCommitMarker?.({
       reason: "manual-delete-current-idb",
       immediate: true,
+      resetAcceptedRevision: true,
     });
     runtime.syncGraphLoadFromLiveContext?.({
       source: "manual-delete-current-idb",
@@ -1252,6 +1253,7 @@ export async function onDeleteAllIdbController(runtime) {
       runtime.clearCurrentChatCommitMarker?.({
         reason: "manual-delete-all-idb",
         immediate: true,
+        resetAcceptedRevision: true,
       });
       runtime.syncGraphLoadFromLiveContext?.({
         source: "manual-delete-all-idb",