fix: patch scaffold URL parser to support self-hosted Gitea (.eu TLD)

zotero-plugin-scaffold hardcodes a .com-only regex in parseRepoUrl,
causing build failures with non-.com repository URLs. Add:
- scripts/patch-scaffold.mjs: postinstall script that fixes the regex
- zotero-plugin.config.ts: explicit xpiDownloadLink and updateURL
  so scaffold generates correct update.json without relying on the parser

package.json

@@ -17,7 +17,8 @@
     "lint": "eslint src",
     "lint:fix": "eslint src --fix",
     "format": "prettier --write \"src/**/*.ts\" \"addon/**/*.js\"",
-    "format:check": "prettier --check \"src/**/*.ts\" \"addon/**/*.js\""
+    "format:check": "prettier --check \"src/**/*.ts\" \"addon/**/*.js\"",
+    "postinstall": "node scripts/patch-scaffold.mjs"
   },
   "repository": {
     "type": "git",