v0.16.0

• New provider: Google Antigravity (agy), with backend, MCP, UI, mobile, infra, and docs parity
• New provider: GitHub Copilot CLI (copilot), with deterministic session binding, UI, mobile, and session-start lifecycle hooks
• Gemini CLI provider retired; templates now redirect to Antigravity (agy)
• E2EE hardening: paired-device dedup (supersede-by-install-id, revoke-on-logout) plus a QR-pairing first-start race fix with in-session self-heal
• Mobile chat: agent busy dots moved into the chat header with an idle state
• Codex: startup update-check disabled at launch