Switch to Manifest V2 for Firefox; convert background to non-module, add global aria2 helpers, and use browserAction badges

manifest.json

@@ -1,9 +1,9 @@
 {
-  "manifest_version": 3,
+  "manifest_version": 2,
   "name": "Archive.org Link Grabber",
   "version": "0.1.0",
   "description": "Filter and export archive.org /download links; copy or send to aria2 RPC.",
-  "action": {
+  "browser_action": {
     "default_title": "Archive.org Link Grabber",
     "default_popup": "src/popup/index.html"
   },
@@ -15,16 +15,16 @@
     "storage",
     "clipboardWrite",
     "activeTab",
-    "contextMenus"
-  ],
-  "host_permissions": [
+    "contextMenus",
     "https://archive.org/*",
     "http://localhost:6800/*",
     "https://localhost:6800/*"
   ],
   "background": {
-    "service_worker": "src/background/index.js",
-    "type": "module"
+    "scripts": [
+      "src/lib/aria2-bg.js",
+      "src/background/index.js"
+    ]
   },
   "content_scripts": [
     {