Fix JSONB fields returned as strings from database

Parse JSONB fields (provenance, origin, tags, metadata, object_data, signature)
if they come back as strings instead of dicts.

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

db.py

@@ -317,6 +317,13 @@ def _parse_asset_row(row) -> dict:
         asset["created_at"] = asset["created_at"].isoformat()
     if asset.get("updated_at"):
         asset["updated_at"] = asset["updated_at"].isoformat()
+    # Ensure JSONB fields are dicts (handle string case)
+    for field in ("tags", "metadata", "provenance", "origin"):
+        if isinstance(asset.get(field), str):
+            try:
+                asset[field] = json.loads(asset[field])
+            except (json.JSONDecodeError, TypeError):
+                pass
     return asset
 
 
@@ -413,6 +420,13 @@ def _parse_activity_row(row) -> dict:
     # Convert datetime to ISO string
     if activity.get("published"):
         activity["published"] = activity["published"].isoformat()
+    # Ensure JSONB fields are dicts (handle string case)
+    for field in ("object_data", "signature"):
+        if isinstance(activity.get(field), str):
+            try:
+                activity[field] = json.loads(activity[field])
+            except (json.JSONDecodeError, TypeError):
+                pass
     return activity