fix(tags): case-insensitive kind prefix + (Fandom) suffix rescue on add

parse_kind_prefix now lowercases the prefix before checking KNOWN_KINDS,
matching the modal JS which already lowercases before its visibility
check. Without this, typing 'Character:Jinx ...' showed the fandom
picker but the server fell back to kind=user.

Both /tags/add and /api/images/bulk-add-tag now also split a trailing
'(Fandom)' suffix from a typed character name when no explicit fandom
is staged, so a manual entry like 'Character:Jinx (League Of Legends)'
produces a clean (name='Jinx', fandom_id=<league>) row instead of a
malformed character with the suffix baked into the name.

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

app/utils/tag_prefix.py

@@ -25,6 +25,11 @@ KNOWN_KINDS: frozenset[str] = frozenset({
 def parse_kind_prefix(raw: str) -> tuple[str | None, str]:
     """Split a raw user-typed tag string into (kind, name).
 
+    The kind prefix is matched case-insensitively so 'Character:' and
+    'CHARACTER:' resolve the same as 'character:'. The returned kind is
+    always lowercase canonical form. The modal JS already lowercases
+    before its own prefix check; this keeps the server in sync.
+
     Returns:
         (kind, name) where kind is one of KNOWN_KINDS, or
         (None, raw.strip()) if no recognized prefix is present.
@@ -32,12 +37,14 @@ def parse_kind_prefix(raw: str) -> tuple[str | None, str]:
 
     Examples:
         parse_kind_prefix('character:Saber')  -> ('character', 'Saber')
+        parse_kind_prefix('Character:Saber')  -> ('character', 'Saber')
         parse_kind_prefix('sunset')           -> (None, 'sunset')
         parse_kind_prefix('http://example')   -> (None, 'http://example')
         parse_kind_prefix('artist: Eric ')    -> ('artist', 'Eric')
     """
     if ':' in raw:
         prefix, rest = raw.split(':', 1)
-        if prefix in KNOWN_KINDS:
-            return prefix, rest.strip()
+        prefix_lower = prefix.lower()
+        if prefix_lower in KNOWN_KINDS:
+            return prefix_lower, rest.strip()
     return None, raw.strip()