Catch migration exceptions so app doesn't crash-loop on startup

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

app/main.py

@@ -15,7 +15,10 @@ async def lifespan(app: FastAPI):
     ok, msg = check_db()
     if ok:
         logger.info("Database connection OK")
-        run_migrations()
+        try:
+            run_migrations()
+        except Exception:
+            logger.exception("Migration failed — app will start but DB schema may be out of date")
     else:
         logger.warning("Database unreachable: %s", msg)
     yield