Release-prep bump across the Claude Code, Codex, and Gemini manifests.
Cutting v4.3.0 also fixes#33: gemini extensions install pulls the latest
GitHub release, and gemini-extension.json was added after v4.2.0, so it
was missing from the release tarball. Shipping it in a release fixes the
plain install command.
Co-authored-by: Claude Opus 4.8 (1M context) <noreply@anthropic.com>