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 interface layer every game shares: the toolbar, the in-game menu, the save indicator, notifications and the common look of panels, buttons and lists.",
-  "category": "ui",
+  "categories": ["ui"],
   "depends": [],
   "sources": [
     "src/**/*.cs"