[Feature Request] Restrict shift+tab permission-mode cycle to a configured subset (e.g. plan ↔ auto only)

Feature request

A settings key to restrict which permission modes shift+tab (chat:cycleMode) cycles through, e.g.:

{
  "permissions": {
    "availableModes": ["plan", "auto"]
  }
}

Motivation

My workflow only ever uses plan and auto. The full cycle is default → acceptEdits → plan → auto, so toggling back from auto to plan takes 3 presses through two modes I never use — and overshooting lands me in a mode I didn't want.

Current state (verified against docs)

• permissions.disableAutoMode and permissions.disableBypassPermissionsMode exist, but there is no equivalent for default/acceptEdits and no whitelist.
• ~/.claude/keybindings.json only exposes chat:cycleMode; there are no per-mode set/toggle actions to build a custom toggle from.
• Managed settings can pin defaultMode but cannot restrict the cycle.

Prior art

This was previously requested in #32604 (and duplicates #49711, #48363), which was auto-closed as stale with users still +1-ing it. The stale-bot suggested opening a new issue if still relevant — it is.

Either an availableModes allowlist or per-mode keybinding actions (chat:setMode:plan etc.) would solve it.