Add dev-prod harmonize tool for bidirectional catalog and image sync.

Schema migrates dev to prod only; catalog rows merge by updated_at and images by mtime with union merge and conflict reporting.

Co-authored-by: Cursor <cursoragent@cursor.com>

db/migrate-sync-timestamps.sql

@@ -0,0 +1,39 @@
+-- Catalog row timestamps for dev/prod harmonize (last-write-wins merge).
+-- Idempotent: safe to re-run on existing databases.
+
+CREATE OR REPLACE FUNCTION sync_touch_updated_at()
+RETURNS TRIGGER AS $$
+BEGIN
+  NEW.updated_at = now();
+  RETURN NEW;
+END;
+$$ LANGUAGE plpgsql;
+
+DO $$
+DECLARE
+  tbl TEXT;
+BEGIN
+  FOREACH tbl IN ARRAY ARRAY[
+    'historical_eras',
+    'art_movements',
+    'artists',
+    'artist_periods',
+    'paintings',
+    'painting_influences',
+    'painting_influence_sources',
+    'painting_annotations'
+  ]
+  LOOP
+    EXECUTE format(
+      'ALTER TABLE %I ADD COLUMN IF NOT EXISTS updated_at TIMESTAMPTZ NOT NULL DEFAULT now()',
+      tbl
+    );
+
+    EXECUTE format('DROP TRIGGER IF EXISTS %I ON %I', tbl || '_updated_at', tbl);
+    EXECUTE format(
+      'CREATE TRIGGER %I BEFORE UPDATE ON %I FOR EACH ROW EXECUTE PROCEDURE sync_touch_updated_at()',
+      tbl || '_updated_at',
+      tbl
+    );
+  END LOOP;
+END $$;