Add telegram channel plugin (#735)

Telegram messaging bridge for Claude Code. Runs a local MCP server that
connects to the Telegram Bot API via a user-created bot token.

Built-in access control: inbound messages are gated by an allowlist
(default: pairing mode), outbound sends are scoped to the same allowlist.
The /telegram:access skill manages pairing, allowlists, and policy.

Ships full source — server.ts runs locally via bun, started by the
.mcp.json command. First external_plugins entry to bundle source rather
than point at a hosted MCP endpoint.

external_plugins/telegram/.mcp.json

@@ -0,0 +1,8 @@
+{
+  "mcpServers": {
+    "telegram": {
+      "command": "bun",
+      "args": ["run", "--cwd", "${CLAUDE_PLUGIN_ROOT}", "--shell=bun", "--silent", "start"]
+    }
+  }
+}