refactor(main): _ensure_fandom_tag stores bare names

Post-migration tag.name no longer embeds 'fandom:' prefix. Helper now
creates/finds by (kind='fandom', name=bare).

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

app/main.py

@@ -26,15 +26,14 @@ def _parse_character_fandom(name_after_prefix):
 
 
 def _ensure_fandom_tag(fandom_name):
-    """Find or create a fandom tag by name. Returns the Tag object.
+    """Find or create a fandom tag by bare name. Returns the Tag object.
 
     Normalizes the display name so callers don't have to remember.
     """
     normalized = normalize_display_name(fandom_name.strip())
-    full_name = f"fandom:{normalized}"
-    fandom_tag = Tag.query.filter_by(name=full_name).first()
+    fandom_tag = Tag.query.filter_by(kind='fandom', name=normalized).first()
     if not fandom_tag:
-        fandom_tag = Tag(name=full_name, kind="fandom")
+        fandom_tag = Tag(kind='fandom', name=normalized)
         db.session.add(fandom_tag)
         db.session.flush()
     return fandom_tag