feat(kg): add tsvector FTS, entity deduplication, and embedding fixes

- Replace ILIKE search with PostgreSQL tsvector/GIN full-text search
  for KG entities (migration 000031)
- Add entity deduplication system with dual-threshold strategy:
  auto-merge at 0.98+ similarity with Jaro-Winkler name match,
  flag 0.90-0.98 as candidates for manual review
- Add ScanDuplicates for bulk on-demand duplicate detection
- Add MergeEntities with advisory lock and tenant-scoped relation
  re-pointing (delete-then-update to avoid ON CONFLICT on UPDATE)
- Wire dedup inline after KG extraction pipeline
- Fix BackfillKGEmbeddings: was failing silently due to
  context.Background() missing tenant_id; now runs cross-tenant
- Fix BackfillKGEmbeddings: break on error → continue with failed
  ID tracking and max consecutive error cap
- Add EmbedEntity helper; UpsertEntity now generates embeddings
  in background goroutine
- Add HTTP endpoints: POST /kg/dedup/scan, GET /kg/dedup,
  POST /kg/merge, POST /kg/dedup/dismiss
- Add web UI: Dedup dialog with Scan All button, side-by-side
  entity comparison, merge/dismiss actions
- Add Jaro-Winkler similarity algorithm with 34 unit tests
- Update IngestExtraction to return upserted entity IDs
- Bump RequiredSchemaVersion to 31

internal/tools/knowledge_graph_test.go

@@ -89,14 +89,34 @@ func (m *mockKGStore) Traverse(_ context.Context, _, _, startEntityID string, _
 	return m.traversal[startEntityID], nil
 }
 
-func (m *mockKGStore) IngestExtraction(context.Context, string, string, []store.Entity, []store.Relation) error {
-	return nil
+func (m *mockKGStore) IngestExtraction(context.Context, string, string, []store.Entity, []store.Relation) ([]string, error) {
+	return nil, nil
 }
 
 func (m *mockKGStore) PruneByConfidence(context.Context, string, string, float64) (int, error) {
 	return 0, nil
 }
 
+func (m *mockKGStore) DedupAfterExtraction(context.Context, string, string, []string) (int, int, error) {
+	return 0, 0, nil
+}
+
+func (m *mockKGStore) ScanDuplicates(context.Context, string, string, float64, int) (int, error) {
+	return 0, nil
+}
+
+func (m *mockKGStore) ListDedupCandidates(context.Context, string, string, int) ([]store.DedupCandidate, error) {
+	return nil, nil
+}
+
+func (m *mockKGStore) MergeEntities(context.Context, string, string, string, string) error {
+	return nil
+}
+
+func (m *mockKGStore) DismissCandidate(context.Context, string, string) error {
+	return nil
+}
+
 func (m *mockKGStore) Stats(context.Context, string, string) (*store.GraphStats, error) {
 	return &store.GraphStats{}, nil
 }