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": "The main menu: start or continue a game, pick one of the installed games, load a save and change the language, sound and display settings.",
-  "category": "ui",
+  "categories": ["ui"],
   "sources": [
     "src/**/*.cs"
   ],