Nightly run: version bump and changelog merges

What's Changed

• Changelog for v0.55.0-preview.1 by @gemini-cli-robot in https://github.com/google-gemini/gemini-cli/pull/28706
• chore(release): bump version to 0.56.0-nightly.20260806.g761f604c1 by @gemini-cli-robot in https://github.com/google-gemini/gemini-cli/pull/28707
• Changelog for v0.54.0 by @gemini-cli-robot in https://github.com/google-gemini/gemini-cli/pull/28708

Full Changelog: https://github.com/google-gemini/gemini-cli/compare/v0.55.0-nightly.20260806.g761f604c1...v0.56.0-nightly.20260807.gd5c9a97dc