fix(grok): address adversarial-review findings across the grok-CLI conversion

A 7-dimension adversarial review (find -> independently refute) surfaced 14 real
issues; fixed each:

Runtime bugs
- GrokCliSession.send drained stdout fully BEFORE stderr — a >64KB stderr burst
  would deadlock the turn forever (spinner never clears). Drain stderr
  concurrently, and add a per-turn watchdog (ROBOCO_GROK_TURN_TIMEOUT_SECONDS,
  default 600s) that kills a wedged process and emits error+turn_end.
- Crash-restarted grok agents launched `grok -p ""` (empty prompt) — Claude gets
  a scan-for-work fallback. Default the prompt in _spawn_container so every
  dedicated provider gets it too.
- _grok_usage_json read /data/grok-usage unconditionally while its writers branch
  compose-vs-local, so a local-mode agent finalized at $0 and the cost-cap was
  inert. Single-source the path in a new _grok_usage_dir helper (read == write).
- GrokCliSession secretary role fell through to "unknown" (get_agent_role returns
  a truthy sentinel, never None), defeating the ROBOCO_AGENT_ROLE fallback.

Parity / hardening
- --deny set was missing `git tag -d` / `git reflog delete` that the Claude
  bash-guard blocks — added them (the "same set" claim is now true).
- Interactive mains now install the bash-guard hook too (defense-in-depth).
- Compose: collapse the GROK_AUTH_DIR / ROBOCO_HOST_GROK_DIR auth-mount pair into
  one canonical var so a partial override can't silently break agent auth.

Docs / comments
- Panel routing card + architecture security doc no longer say Grok runs on the
  deleted opencode runtime; orchestrator comments point at the renamed entrypoint.

Tests
- Cover the interactive _render_grok_config MCP wiring (ModuleNotFound guard +
  secretary HMAC env), the cost-cap kill-failure + interactive relay-close paths,
  the local-mode usage read, the role fallback, the turn timeout, and the new
  git denies. (#13 — a separate grok "Write" tool — investigated: grok's only
  built-in file-mutation tool is search_replace, already removed; no gap.)

Gate green: ruff, mypy, xenon, tests.

.env.example

@@ -91,11 +91,10 @@ ROBOCO_DEFAULT_EMBEDDING_MODEL=qwen3-embedding:0.6b
 # the CLI authenticates from a mounted ~/.grok/auth.json — run `grok login` once
 # on the host (auth.json auto-refreshes). Every var below is optional.
 
-# Host dir holding the SuperGrok auth. The orchestrator mounts <dir>/auth.json
-# read-only into each Grok agent's ~/.grok. GROK_AUTH_DIR is the host source the
-# compose mounts into the orchestrator; keep both equal to the host's ~/.grok.
+# Host dir holding the SuperGrok auth (one canonical var). The compose mounts it
+# into the orchestrator at the same path, and the orchestrator hands that path to
+# each Grok agent's auth.json bind — so it must be the real host ~/.grok.
 # ROBOCO_HOST_GROK_DIR=/home/youruser/.grok
-# GROK_AUTH_DIR=/home/youruser/.grok
 
 # Image the orchestrator spawns for Grok agents, and the CLI model id.
 # ROBOCO_GROK_AGENT_IMAGE=roboco-agent-grok:latest