Codex and Antigravity tabs, behind their own version floors

Two more CLI runtimes in the workbench, each gated on the daemon actually being able to serve it — and refusing in words when it can't.

The new-tab picker now offers Codex and Antigravity alongside Claude Code, but only on machines whose daemon can actually run them. Each runtime sits behind its own floor: the daemon reports its version, the server checks it, and creating a tab it can’t serve fails with a sentence rather than a stack trace.

Adoption is per-CLI — a Codex session resumes by thread id, an Antigravity tab keeps the session’s runtime when adopted. DAEMON_LATEST moved 0.44.1 → 0.48.2 across the sweep; the minimum floor didn’t have to move with it, because every new capability gates itself.