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/src/core/index.ts

@@ -3,4 +3,5 @@ export * from './throttle';
 export * from './scripting';
 export * from './tab-helpers';
 export * from './group-helpers';
+export * from './tab-groups';
 export * from './storage';