Firefox experimental warning and v0.4.1 release packaging

[kbuffardi]

Summary

• Show Firefox users only this terminal warning on load: Firefox support is still experimental. Brave, Chrome, Chromium, or Edge browsers are recommended.
• Stop generating the unsigned Firefox ZIP release artifact while preserving Firefox build, smoke, and protected unlisted-XPI signing paths.
• Bump the project version to 0.4.1.

Acceptance criteria

• Firefox compatibility output is exactly the requested sentence.
• Release packaging emits Chrome, Edge, Brave, and Chromium ZIPs, but no Firefox ZIP.
• manifest.json, package.json, and package-lock.json versions are synchronized at 0.4.1.
• Existing tests, lint, build, and release checks pass.

[kbuffardi]

Implementation plan (plan-agent):

1. Add a regression test for the exact Firefox terminal warning and update Firefox compatibility-report expectations without changing Chromium behavior.
2. Mark Firefox non-publishable in release target metadata so package:release emits no Firefox ZIP, while retaining dist-firefox generation, Firefox smoke validation, and protected unlisted-XPI signing. Update release packaging assertions and release documentation.
3. Bump manifest.json to 0.4.1 and synchronize package.json/package-lock.json.
4. Run targeted tests, full E2E, lint, build, and version/release checks.

Acceptance: Firefox startup output is exactly the requested sentence; only Chrome/Edge/Brave/Chromium ZIPs are generated; all version metadata is 0.4.1.

[kbuffardi]

Implemented on branch chore/firefox-experimental-v041 and opened PR #60.

The Firefox terminal formatter now emits only the requested experimental-support sentence; Firefox remains build/smoke/signing-capable but is excluded from release ZIP generation; version metadata is synchronized at 0.4.1. Verification passed: lint, build, 177 E2E tests, Firefox web-ext smoke, version checks, release check, and release packaging with Chrome/Edge/Brave/Chromium ZIPs only.