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>

src/config/dependency-registry.ts

@@ -8,6 +8,7 @@
  */
 
 import { PI_VERSION_REGEX } from '../utils/pi-cli-resolver.js';
+import { GROK_VERSION_REGEX } from '../utils/grok-cli-resolver.js';
 
 export type ProbeEnvironment = 'linux' | 'darwin' | 'win32' | 'wsl';
 
@@ -139,6 +140,29 @@ export const DEPENDENCY_REGISTRY: ToolDependency[] = [
       },
     ],
   },
+  {
+    id: 'grok',
+    label: 'Grok CLI',
+    category: 'core',
+    required: false,
+    usedBy: ['Grok sessions'],
+    // Version match required for the same reason as pi: `grok` has known squatters
+    // (the unrelated @vibe-kit/grok-cli npm package also installs a `grok` bin), so a
+    // bare `which grok` hit is not the coding agent. Both sides share
+    // GROK_VERSION_REGEX, so the doctor and the run mode cannot drift.
+    resolvers: [
+      {
+        match: ALL,
+        resolver: {
+          kind: 'path',
+          bins: ['grok'],
+          versionArg: '--version',
+          versionRegex: GROK_VERSION_REGEX,
+          requireVersionMatch: true,
+        },
+      },
+    ],
+  },
   {
     id: 'libreoffice',
     label: 'LibreOffice',