fix(tag-prefix): drop artist/meta/rating from KNOWN_KINDS — artist tags retired in FC-2d-vii-c (provenance is its own axis), meta/rating retired by operator 2026-05-26. User-typeable prefixes now just character/fandom/series. Frontend placeholder + icon map + client-side mirror updated; new test confirms retired prefixes parse as literal text.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

backend/app/utils/tag_prefix.py

@@ -10,15 +10,18 @@ KNOWN_KINDS keeps its colon as literal text.
 from __future__ import annotations
 
 # Kinds the user can type as a prefix at the input boundary.
-# `general` is intentionally excluded — it's the default for un-prefixed
-# input. `archive` and `post` are system-managed and never user-typed.
+# Exclusions:
+#   - `general` is the default for un-prefixed input (never typed as prefix)
+#   - `archive`, `post` are system-managed
+#   - `artist` was retired in FC-2d-vii-c — artists are first-class
+#     entities (Artist row + ImageRecord.artist_id), browsed via the
+#     provenance axis rather than as tags. See project_provenance_separation.
+#   - `meta`, `rating` retired as user-typeable per operator 2026-05-26 —
+#     content classification only needs character/fandom/series.
 KNOWN_KINDS: frozenset[str] = frozenset({
-    "artist",
     "character",
     "fandom",
     "series",
-    "meta",
-    "rating",
 })