feat: enable webextension builds

Currently only supports Chrome due to no `chrome` -> `browser` polyfill

src/manifest.json

@@ -4,14 +4,34 @@
   "author": EXTENSION_AUTHOR,
   "manifest_version": 3,
   "version": EXTENSION_VERSION,
+  "permissions": [
+    "storage",
+    "scripting"
+  ],
+  "host_permissions": [
+    "https://wiki.teamfortress.com/wiki/*",
+    "https://*.prices.tf/*",
+    "https://open.er-api.com/*"
+  ],
+  "web_accessible_resources": [
+    {
+      "resources": ["lib/style.css", "resources/*"],
+      "matches": ["https://wiki.teamfortress.com/*"]
+    }
+  ],
   "content_scripts": [
     {
       "matches": ["*://wiki.teamfortress.com/wiki/*"],
       "run_at": "document_start",
       "all_frames": true,
+      "css": ["lib/style.css"],
       "js": ["content/content.js"]
     }
   ],
+  "background": {
+    "service_worker": "background/background.js",
+    "type": "module"
+  },
   "icons": {
     "48": "icons/icon-48.png",
     "96": "icons/icon-96.png"