feat(channels): add Telegram channel integration with ACP bridge

Implements the channels infrastructure for connecting external messaging
platforms to Qwen Code via ACP. Phase 1 supports plain text round-trip:
Telegram user sends message -> AcpBridge -> qwen-code --acp -> response
back to Telegram.

New packages:
- @qwen-code/channel-base: AcpBridge, SessionRouter, SenderGate, ChannelBase
- @qwen-code/channel-telegram: TelegramAdapter using telegraf

CLI: `qwen channel start <name>` reads from settings.json channels config,
spawns ACP agent, connects to Telegram via polling.

package.json

@@ -6,7 +6,9 @@
   },
   "type": "module",
   "workspaces": [
-    "packages/*"
+    "packages/*",
+    "packages/channels/base",
+    "packages/channels/telegram"
   ],
   "repository": {
     "type": "git",