Add Firefox target and clean command

v0.2.0 — Firefox Support & New CLI Commands

Firefox Target

• --target firefox flag on cargo oxichrome build — generates a Firefox-compatible Manifest V3 extension
  • Background uses "scripts" instead of "service_worker"
  • Adds browser_specific_settings.gecko.id (derived from extension name, e.g. my-extension@oxichrome.dev)
  • CSP remains object format for MV3 compatibility on both browsers
• --target chromium (default) — unchanged Chrome/Brave/Edge output
• Build output is now separated: dist/chromium/ and dist/firefox/ so both targets coexist

New CLI Commands

• cargo oxichrome clean — removes the dist/ directory

Project Metadata

• Bumped all crate versions to 0.2.0
• Added homepage = "https://oxichrome.dev" to all crate manifests
• Updated README to reflect new changes