feat: add iMessage channel, channels setup guide, 3-way distinction

- messaging/channels-setup.md: comprehensive guide covering all 3
  channels (Telegram, Discord, iMessage), bun install, plugin setup,
  session persistence workarounds, and enterprise admin settings
- messaging/imessage-setup.md: macOS-specific iMessage setup with
  Full Disk Access, /imessage access allow, and known quirks
- messaging/README.md: rewritten with 3-way distinction table
  (Channels=event-based, Dispatch=message-based, RC=direct control)
- examples/12: expanded from 2 options to 3 with clear trigger model
- feature-map.md: row 9 updated to include iMessage
- README.md: session persistence warning added as top-level section

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

feature-map.md

@@ -24,7 +24,7 @@ and Dispatch.
 | 6 | Computer Use | Browser + desktop app control | Computer Use in CC Desktop + Cowork (research preview) | ✅ |
 | 7 | Memory | Daily logs + vector search | CLAUDE.md hierarchy + auto-memory | ~ |
 | 8 | Multi-Agent | Sub-agents, mesh, agent-to-agent | Agent Teams, SendMessage, worktree | ✅ |
-| 9 | Messaging/Remote | 15+ native channels | MCP + Telegram (v2.1.80) + Remote Control (/rc) + Dispatch | ~ |
+| 9 | Messaging/Remote | 15+ native channels | Channels (Telegram, Discord, iMessage) + MCP + /rc + Dispatch | ~ |
 | 10 | Model Providers | 20+ providers, failover | Opus/Sonnet/Haiku + overrides | ~ |
 | 11 | Cron/Automation | HEARTBEAT.md, cron, webhooks | /loop, CronCreate, /schedule, hooks | ✅ |
 | 12 | Always-On | Daemon process, 24/7 | Headless on VPS + Cowork "keep awake" + /schedule | ~ |