Add updated_at column and trigger for Qdrant re-sync detection

Adds updated_at TIMESTAMPTZ to ocr_jobs, stamped automatically by a
BEFORE UPDATE trigger. The sync process can use updated_at > qdrant_synced_at
to detect jobs that need re-ingestion after edits or reviews.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

backend/database.py

@@ -58,6 +58,25 @@ def init_db():
                 ALTER TABLE ocr_jobs
                 ADD COLUMN IF NOT EXISTS qdrant_synced_at TIMESTAMPTZ
             """)
+            cur.execute("""
+                ALTER TABLE ocr_jobs
+                ADD COLUMN IF NOT EXISTS updated_at TIMESTAMPTZ
+            """)
+            # Trigger function: stamp updated_at on every row update
+            cur.execute("""
+                CREATE OR REPLACE FUNCTION set_updated_at()
+                RETURNS TRIGGER AS $$
+                BEGIN
+                    NEW.updated_at = NOW();
+                    RETURN NEW;
+                END;
+                $$ LANGUAGE plpgsql
+            """)
+            cur.execute("""
+                CREATE OR REPLACE TRIGGER ocr_jobs_set_updated_at
+                BEFORE UPDATE ON ocr_jobs
+                FOR EACH ROW EXECUTE FUNCTION set_updated_at()
+            """)
             # Unique constraint: prevent duplicate (author, chapter, page) submissions.
             # Applies only when all three fields are non-null.
             cur.execute("""