replace Redis with an embedded SQLite string->string KV store (group commit, in-tx events, SQL search)

internal/api/metadata.go

@@ -40,9 +40,9 @@ type MetadataSearchRequest struct {
 	Limit         int    `json:"limit,omitempty"`
 
 	// Filters is the structured form: AND across entries, OR within an
-	// entry's Values. Evaluated in memory against the search index alongside
-	// the free-text Query, so an id-anchored lookup costs a map probe per
-	// record rather than a Redis round-trip per record.
+	// entry's Values. Narrowed in SQL through the field index alongside the
+	// free-text Query, then verified per record (see serveIndexedSearch), so an
+	// id-anchored lookup costs an index probe rather than a read per record.
 	//
 	// Property/PropertyValue is the single-filter legacy shape and folds into
 	// this list (see normalizedFilters) with Exact=false, preserving its
@@ -445,9 +445,8 @@ func (s *Server) handleSearchMetadata(w http.ResponseWriter, r *http.Request) {
 	}
 
 	// Everything else — free text, structured filters, both, or neither
-	// (which returns the first `limit`) — is served from the in-memory search
-	// index (search_index.go). Matching and the returned metadata both come
-	// from memory, so a query costs zero Redis round-trips.
+	// (which returns the first `limit`) — is served from the store's derived
+	// search indexes (search_index.go → storage.Search).
 	//
 	// There is deliberately no second path. The property branch used to fall
 	// through to a `GetAllHashIDs` + per-record `GetMetadataFlat` scan, which