chore: release 3.16.0

[joshuawheelock]

Changed

• Antigravity agent support: Replaced Gemini CLI initialization and worker-agent support with Antigravity CLI support using the documented agy executable, .agents/skills, and .agents/hooks.json hook surface.

Removed

• Gemini agent support: Removed Gemini as a selectable initialization and worker agent target, including obsolete Gemini settings fragments, configurers, command mappings, and logo assets.
• Co-located evals project: Removed the evals/ directory from this repository; the eval framework now lives in its own repository rather than as a nested npm project here.