feat(v2): add pre-task script hook for scheduled tasks

Scheduled tasks can now carry a bash script that runs inside the container
before the agent is invoked. The script prints `{wakeAgent, data?}` on its
last stdout line; if `wakeAgent: false` (or the script errors) the task
row is marked completed and the agent is never queried, saving API calls
on no-op checks. On wake, the script's `data` is injected into the task
prompt. Semantics mirror V1: 30s bash timeout, 1MB buffer, last-line JSON,
error == skip.

Also blocks the Claude SDK's built-in scheduling tools (CronCreate,
CronDelete, CronList, ScheduleWakeup) via `disallowedTools` so tasks
actually flow through `mcp__nanoclaw__schedule_task` and get the script
gate. CLAUDE.md gains a soft pointer explaining why `schedule_task` is
the right path.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

groups/global/CLAUDE.md

@@ -126,7 +126,9 @@ request_rebuild({ reason: "Add memory MCP server" })
 
 ## Task Scripts
 
-For any recurring task, use `schedule_task`. Frequent agent invocations — especially multiple times a day — consume API credits and can risk account restrictions. If a simple check can determine whether action is needed, add a `script` — it runs first, and the agent is only called when the check passes. This keeps invocations to a minimum.
+For any recurring task, use `schedule_task`. This is the scheduling path — tasks persist across sessions and restarts, and support the pre-task `script` hook described below. Other scheduling tools you might discover (e.g. `CronCreate`, `ScheduleWakeup`) are session-scoped SDK builtins and won't behave the way NanoClaw users expect, so stick with `schedule_task`.
+
+Frequent agent invocations — especially multiple times a day — consume API credits and can risk account restrictions. If a simple check can determine whether action is needed, add a `script` — it runs first, and the agent is only called when the check passes. This keeps invocations to a minimum.
 
 ### How it works