Add fakechat channel plugin (#738)

Localhost web chat UI for testing the channel notification flow.
No tokens, no access control, no third-party service. Serves an
iMessage-style UI on localhost; messages posted there arrive as
channel notifications, replies render in the UI.

Useful for developing against the channel protocol without a live
messaging account.

Ships full source — server.ts runs locally via bun, started by the
.mcp.json command.

external_plugins/fakechat/package.json

@@ -0,0 +1,16 @@
+{
+  "name": "claude-channel-fakechat",
+  "version": "0.0.1",
+  "license": "Apache-2.0",
+  "type": "module",
+  "bin": "./server.ts",
+  "scripts": {
+    "start": "bun install --no-summary && bun server.ts"
+  },
+  "dependencies": {
+    "@modelcontextprotocol/sdk": "^1.0.0"
+  },
+  "devDependencies": {
+    "@types/bun": "^1.3.10"
+  }
+}