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>

README.md

@@ -62,7 +62,7 @@ Paste the prompt from examples/01-agent-runtime/prompt.md
 | `security/` | Permission modes, Auto Mode, hook patterns, NemoClaw comparison |
 | `memory/` | How Claude Code memory works vs OpenClaw's vector search |
 | `automation/` | Cron, launchd, /loop, /schedule |
-| `messaging/` | Slack MCP, Telegram Channels, channel comparison |
+| `messaging/` | Channels (iMessage, Telegram, Discord), Slack MCP, Dispatch/RC comparison |
 | `browser/` | Playwright MCP setup and usage |
 | `cowork-integration/` | How Code + Cowork + Dispatch together replicate OpenClaw |
 
@@ -81,7 +81,7 @@ Paste the prompt from examples/01-agent-runtime/prompt.md
 | 09 | Security Hooks | PreToolUse/PostToolUse | Exec approvals + Docker |
 | 10 | Full Pipeline | All capabilities combined | Complete workflow |
 | 11 | Computer Use | Control desktop apps | macOS/iOS/Android apps |
-| 12 | Remote Control | /rc + Dispatch (phone) | Telegram/WhatsApp control |
+| 12 | Remote Access | Channels + Dispatch + /rc (3 ways) | Telegram/WhatsApp control |
 | 13 | Auto Mode | AI safety classifier | Autonomous daemon mode |
 
 Each example has a self-contained prompt you can paste directly
@@ -111,6 +111,15 @@ See [cowork-integration/README.md](cowork-integration/README.md)
 for a detailed breakdown of how these combine to cover OpenClaw's
 feature set.
 
+## The biggest practical limitation
+
+**Session persistence.** If the Claude Code session closes, all
+remote access (Channels, Dispatch, Remote Control) stops. OpenClaw
+runs as a daemon and stays alive indefinitely. Workarounds exist
+(tmux, Mac Mini, VPS), but this is an architectural difference.
+
+See `messaging/channels-setup.md` for always-on workarounds.
+
 ## The remaining gap
 
 **Canvas/A2UI (the only gap):** OpenClaw's canvas is an interactive