feat: add Firefox extension support

- Add Firefox as an install target with native messaging manifest support.
- Generate Firefox-specific extension packages with Gecko metadata and AMO-compatible manifest transforms.
- Keep tab group commands available in Firefox through dynamic tab group API helpers.
- Avoid Firefox linter warnings for static tab group API references and direct eval tokens.
- Add Firefox packaging and installer regression coverage.
- Bump the package and extension version to 0.15.1.

extension/manifest.json

@@ -1,8 +1,14 @@
 {
   "manifest_version": 3,
   "name": "browser-cli",
-  "version": "0.14.3",
+  "version": "0.15.1",
   "description": "Control your browser from the terminal or Python SDK",
+  "browser_specific_settings": {
+    "gecko": {
+      "id": "browser-cli@yiprawr.dev",
+      "strict_min_version": "120.0"
+    }
+  },
   "permissions": [
     "tabs",
     "tabGroups",