Add iMessage

NanoClaw talks to iMessage through a single imessage channel with two pluggable backends:

• Local (this Mac), the Chat SDK bridge over chat-adapter-imessage, reading this Mac's signed-in iMessage account (chat.db). macOS only; the Node binary needs Full Disk Access.
• Hosted iMessage (via photon.codes), a native adapter over Photon's spectrum-ts gRPC stream. The hosted service owns the iMessage line, so there's no Mac relay, webhook, or public URL. Works on any OS, and a device-login flow provisions everything for you.

Both register the same imessage channel type; only one runs per install. NanoClaw doesn't ship channels in trunk, this skill copies the unified imessage adapter in from the channels branch. Full reference: docs/imessage.md.

The mechanical steps under Apply carry nc: directive fences: an agent reads the prose and applies them, and a parser can apply them deterministically from the same document. Every directive is idempotent, so the whole skill is safe to re-run; anything a parser can't apply falls back to the prose beside it.

Apply

1. Choose a backend

Pick the backend first, it decides which package gets installed and which walkthrough runs below (the other backend's steps are skipped):

How should iMessage run, `local` (this Mac's signed-in iMessage account; macOS only, needs Full Disk Access) or `hosted` (a managed line via photon.codes; works on any OS)?

The local backend only works on a Mac, it reads this machine's iMessage chat.db directly, and there is no such database off macOS. On any other OS, stop here and choose hosted instead; otherwise you'd write a local config that can never receive a message:

[ "$(uname)" = Darwin ]

2. Copy the adapter

Fetch the channels branch and copy the unified iMessage adapter and its tests into src/channels/: