feat(extension): add Firefox browser extension and native integration

- Implement Firefox extension to intercept downloads and scrape selected links via context menus
- Create LocalExtensionServer over TCP (localhost:6412) to receive links from the extension
- Automatically package extension to firelink.xpi in create_app_bundle.sh
- Add Integrations tab in SettingsView with one-click installer for Firefox variants
- Modify ContentView and TrayMenuView to automatically open the Add Downloads window on extension trigger

Extensions/Firefox/manifest.json

@@ -0,0 +1,30 @@
+{
+  "manifest_version": 3,
+  "name": "Firelink",
+  "version": "1.0.0",
+  "description": "Capture downloads and links directly to Firelink download manager.",
+  "permissions": [
+    "downloads",
+    "downloads.open",
+    "contextMenus",
+    "storage",
+    "activeTab",
+    "scripting"
+  ],
+  "background": {
+    "scripts": ["background.js"]
+  },
+  "action": {
+    "default_popup": "popup/popup.html",
+    "default_title": "Firelink"
+  },
+  "icons": {
+    "48": "icons/icon-48.png",
+    "128": "icons/icon-128.png"
+  },
+  "browser_specific_settings": {
+    "gecko": {
+      "id": "firelink@nimbold.github.io"
+    }
+  }
+}