fix(backend): get_settings fills missing DEFAULTS keys for stale config documents

backend/app/models/app_settings.py

@@ -53,6 +53,12 @@ async def get_settings() -> dict:
     if not doc:
         await db.app_settings.insert_one(DEFAULTS.copy())
         doc = DEFAULTS.copy()
+    else:
+        # Fill in any keys added to DEFAULTS since the document was first created
+        missing = {k: v for k, v in DEFAULTS.items() if k not in doc}
+        if missing:
+            await db.app_settings.update_one({"_id": "config"}, {"$set": missing})
+            doc.update(missing)
 
     _cache = doc
     _cache_ts = time.monotonic()