fix(gateway): wire Telegram plugin into gateway plugin host

Add @mosaic/telegram-plugin dependency to gateway, implement
TelegramChannelPluginAdapter, replace stub warning with real plugin
instantiation, and document all Phase 5 env vars in .env.example.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

apps/gateway/package.json

@@ -20,6 +20,7 @@
     "@mosaic/coord": "workspace:^",
     "@mosaic/db": "workspace:^",
     "@mosaic/discord-plugin": "workspace:^",
+    "@mosaic/telegram-plugin": "workspace:^",
     "@mosaic/log": "workspace:^",
     "@mosaic/memory": "workspace:^",
     "@mosaic/types": "workspace:^",

apps/gateway/src/plugin/plugin.module.ts

@@ -7,6 +7,7 @@ import {
   type OnModuleInit,
 } from '@nestjs/common';
 import { DiscordPlugin } from '@mosaic/discord-plugin';
+import { TelegramPlugin } from '@mosaic/telegram-plugin';
 import { PluginService } from './plugin.service.js';
 import type { IChannelPlugin } from './plugin.interface.js';
 
@@ -26,9 +27,23 @@ class DiscordChannelPluginAdapter implements IChannelPlugin {
   }
 }
 
+class TelegramChannelPluginAdapter implements IChannelPlugin {
+  readonly name = 'telegram';
+
+  constructor(private readonly plugin: TelegramPlugin) {}
+
+  async start(): Promise<void> {
+    await this.plugin.start();
+  }
+
+  async stop(): Promise<void> {
+    await this.plugin.stop();
+  }
+}
+
 const DEFAULT_GATEWAY_URL = 'http://localhost:4000';
 
-function createPluginRegistry(logger: Logger): IChannelPlugin[] {
+function createPluginRegistry(): IChannelPlugin[] {
   const plugins: IChannelPlugin[] = [];
   const discordToken = process.env['DISCORD_BOT_TOKEN'];
   const discordGuildId = process.env['DISCORD_GUILD_ID'];
@@ -50,8 +65,13 @@ function createPluginRegistry(logger: Logger): IChannelPlugin[] {
   const telegramGatewayUrl = process.env['TELEGRAM_GATEWAY_URL'] ?? DEFAULT_GATEWAY_URL;
 
   if (telegramToken) {
-    logger.warn(
-      `Telegram plugin requested for ${telegramGatewayUrl}, but @mosaic/telegram-plugin is not implemented yet.`,
+    plugins.push(
+      new TelegramChannelPluginAdapter(
+        new TelegramPlugin({
+          token: telegramToken,
+          gatewayUrl: telegramGatewayUrl,
+        }),
+      ),
     );
   }
 
@@ -63,7 +83,7 @@ function createPluginRegistry(logger: Logger): IChannelPlugin[] {
   providers: [
     {
       provide: PLUGIN_REGISTRY,
-      useFactory: (): IChannelPlugin[] => createPluginRegistry(new Logger('PluginModule')),
+      useFactory: (): IChannelPlugin[] => createPluginRegistry(),
     },
     PluginService,
   ],