Fix scheduled tasks and improve task scheduling UX

- Fix Apple Container mount issue: move groups/CLAUDE.md to groups/global/
  directory (Apple Container only supports directory mounts, not file mounts)
- Fix scheduled tasks for main group: properly detect isMain based on
  group_folder instead of always setting false
- Add isScheduledTask flag so agent knows when running as scheduled task
- Improve schedule_task tool description with clear format examples for
  cron, interval, and once schedule types
- Update global CLAUDE.md with instructions for scheduled tasks to use
  mcp__nanoclaw__send_message when needed

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

SPEC.md

@@ -53,7 +53,7 @@ A personal Claude assistant accessible via WhatsApp, with persistent memory per
 │  │  Working directory: /workspace/group (mounted from host)       │   │
 │  │  Volume mounts:                                                │   │
 │  │    • groups/{name}/ → /workspace/group                         │   │
-│  │    • groups/CLAUDE.md → /workspace/global/CLAUDE.md            │   │
+│  │    • groups/global/ → /workspace/global/ (non-main only)        │   │
 │  │    • ~/.claude/ → /home/node/.claude/ (sessions)               │   │
 │  │    • Additional dirs → /workspace/extra/*                      │   │
 │  │                                                                │   │