feat(grok): reasoning-effort by role (cut grok-build cost on cheap roles)

grok-build-0.1 reasons heavily by default and reasoning bills at the output
rate (a live "say ok" call emitted ~300 reasoning tokens, ~85% of its cost).
Confirmed live that opencode's `--variant minimal` cuts reasoning ~54%
(298 -> 136 tokens, same prompt).

GrokProvider now picks reasoning effort by role: code-quality roles (developer,
qa, pr_reviewer) keep full reasoning; coordination / docs / board roles
(cell_pm, main_pm, documenter, product_owner, head_marketing, auditor, prompter,
secretary) run "minimal". It's passed to opencode via the entrypoint's
`--variant`. Operators can force one effort for ALL grok agents with the
ROBOCO_GROK_REASONING_EFFORT env (minimal | high | max, or default/full).

Tests cover the role map, the env override, and the spawn env wiring.

docker/scripts/grok-agent-entrypoint.sh

@@ -20,6 +20,16 @@ python -m roboco.llm.providers.opencode_config
 # `< /dev/null` is REQUIRED: without a closed stdin, `opencode run` hangs after
 # init in a headless / no-TTY environment (it blocks waiting on stdin). Verified
 # live — closing stdin lets the run proceed to the model call and exit cleanly.
+#
+# Reasoning effort: GrokProvider sets ROBOCO_GROK_VARIANT per role (e.g.
+# "minimal" for coordination/docs roles to cut reasoning cost). Absent =
+# opencode default (full reasoning).
+variant_arg=()
+if [ -n "${ROBOCO_GROK_VARIANT:-}" ]; then
+  variant_arg=(--variant "$ROBOCO_GROK_VARIANT")
+fi
+
 exec opencode run \
   --model "xai/${ROBOCO_AGENT_MODEL:-grok-build-0.1}" \
+  "${variant_arg[@]}" \
   -- "${ROBOCO_INITIAL_PROMPT:-}" < /dev/null