fix: enforce case-insensitive genre uniqueness

genres had only case-sensitive name UNIQUE while authors/tags use
UNIQUE (lower(name)); sync_genres could race two case variants into duplicate
rows (audit DB-3). Migration 0038 pre-dedups then adds
UNIQUE (lower(name)); sync_genres upserts ON CONFLICT (lower(name)). Tested.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

frontend/package.json

@@ -1,6 +1,6 @@
 {
   "name": "mangalord-frontend",
-  "version": "0.128.12",
+  "version": "0.128.13",
   "private": true,
   "type": "module",
   "scripts": {