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.

pyproject.toml

@@ -1,6 +1,6 @@
 [project]
 name = "real-browser-cli"
-version = "0.14.3"
+version = "0.15.1"
 description = "Control your real running browser from the terminal or Python SDK"
 readme = "README.md"
 license = { file = "LICENSE" }