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": "Dialog engine: the dialog box with portraits and answers, and the .scenario language in which every game of the collection tells its story.",
-  "category": "engine, library",
+  "categories": ["engine", "library"],
   "sources": [
     "src/**/*.cs"
   ],