feat: use authored category names for mods

Store categories as authored strings. Trim and deduplicate without changing case, compare without case sensitivity, and keep all observed categories available to filters and editors.

manifest.json

@@ -4,7 +4,7 @@
   "version": "0.1.0",
   "author": "ct",
   "description": "Characters engine: heroes, companions and enemies with their battle attributes and action cards, the character actions panel and dialog portraits.",
-  "category": "engine, library",
+  "categories": ["engine", "library"],
   "sources": [
     "src/**/*.cs"
   ],