feat(grok): add Grok Build (xAI) as a seventh CLI run mode

SessionMode gains 'grok', a first-class backend alongside Claude Code,
shell, OpenCode, Codex, Gemini, Antigravity and Pi: its own PTY, tmux
session, charcoal tab identity ('gk' badge), welcome button, run-mode
entry, cron agentType, Docker and remote-SSH command defaults, and
clone-repo Brain option. Flag surface verified live against grok 1.0.5.

Grok mixes two existing shapes and the wiring follows from that:

- Codex-shaped on permissions: the bypass switch is GrokConfig.alwaysApprove
  (--always-approve, grok's bypassPermissions mode; config-level deny rules
  still apply on top). The Run button sends it true, like runAntigravity(),
  and clampExternalCliBypassForOwner() puts grok in the only-if-sent branch:
  a bare grok spawn is grok's own ask-mode default, which is already safe,
  so only a sent config needs the flag forced off. Cron needs nothing for
  the same reason.
- OpenCode-shaped on rendering: grok is a fullscreen alternate-screen TUI
  with mouse support, so it stays OUT of isAltScreenStripMode() and lands
  on the narrow tmux-attach strip and the 'buffer' local-echo fallthrough
  (unmeasured against an authenticated composer; documented fallback is the
  'off' branch).
- Pi-shaped on resolution: 'grok' has npm squatters (@vibe-kit/grok-cli
  also installs a grok bin), so grok-cli-resolver.ts version-probes every
  candidate (grok --version, killSignal SIGKILL, VITEST-gated) and
  GET /api/grok/status surfaces path AND version; GROK_VERSION_REGEX is
  shared with the dependency registry so doctor and run mode cannot drift.

Env allowlist gains GROK_* plus the XAI_* vendor namespace (XAI_API_KEY is
grok's documented headless auth var), the same narrow-vendor reasoning as
GOOGLE_* for gemini. Resume is id-regexed on purpose: grok's own --resume
also matches session titles, which are arbitrary user strings that must
never reach the bash -c spawn line.

Docker: grok is not on npm, so the agent image installs it in its own step
(xAI's installer has no --dir override; the binary is copied to
/usr/local/bin and root's ~/.grok dropped in the same layer), and
credentials are seeded per-file (auth.json, config.toml, pager.toml; the
dir also holds sessions/, memory/ and the ~160MB binary). Remote SSH routes
through the login-shell wrapper like the other agent CLIs.

Verified end to end on an isolated CODEMAN_INSTANCE with grok 1.0.5
installed: /api/grok/status resolves and reports the probed version,
quick-start spawns a pane whose command line ends in 'grok
--always-approve', the real TUI renders (OAuth device screen on an
unauthenticated box), and grokConfig round-trips through state.json.
Docs: docs/grok-integration.md (user guide) + docs/grok-integration-plan.md
(decisions, verification record, follow-ups).

Tests: test/grok-mode.test.ts, test/grok-cli-resolver.test.ts, plus
extended clamp/system-routes/render-index-html/run-mode-ui/mobile-overview/
local-echo-gating coverage. npm test (the CI gate) green: 5910 tests.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

skills/codeman/reference/messaging.md

@@ -56,7 +56,7 @@ own head: the worker enforcing the cap is the one who has to be told about it.
 | synchronize on end of turn | HTTP `wait until=stop` (fires for message-initiated turns too, verified live) |
 | liveness / death check | HTTP `wait?until=exit` |
 | interrupt a running turn (break-glass) | HTTP input, a bare `\x1b` with no `\r` |
-| non-claude modes (`shell`/`opencode`/`codex`/`gemini`/`antigravity`/`pi`) | HTTP only (no other CLI has messaging) |
+| non-claude modes (`shell`/`opencode`/`codex`/`gemini`/`antigravity`/`pi`/`grok`) | HTTP only (no other CLI has messaging) |
 | delete | HTTP, via SKILL.md's `delete_session` guard |
 
 ## Availability: probe, never assume
@@ -347,7 +347,7 @@ Without a break-glass, a pair with a bad brief is a token bonfire with no off sw
 
 ### Mixed fleets: the pairing matrix
 
-Non-claude workers (`shell`, `opencode`, `codex`, `gemini`, `antigravity`, `pi`) cannot be peers
+Non-claude workers (`shell`, `opencode`, `codex`, `gemini`, `antigravity`, `pi`, `grok`) cannot be peers
 at all; no other CLI has this feature. Their tasks route over HTTP, and you never mention
 messaging in their briefs. The claude half of the fleet can use messaging among itself,
 subject to the namespace rule: **messaging works between two sessions that share one