feat: add channel adapter abstraction with Telegram and WebChat adapters

Implement Phase 3 channel adapters that decouple message sources from
the agent via a uniform ChannelAdapter interface and ChannelRegistry.

- Add ChannelAdapter/InboundMessage/OutboundMessage types
- Add ChannelRegistry for adapter lifecycle and message routing
- Add TelegramAdapter (grammy bot, auth middleware, confirmations, chunking)
- Add WebChatAdapter (thin shim over GatewayServer)
- Refactor daemon to use ChannelRegistry with per-channel-per-user agents
- Add config.get/config.patch gateway handlers (Phase 2 loose end)
- Add system.restart gateway handler (Phase 2 loose end)
- Add implementation plans and design docs

Tests: 225 passing (33 new channel adapter + gateway handler tests)

src/gateway/server.ts

@@ -18,8 +18,10 @@ import {
   createSessionHandlers,
   createToolHandlers,
   createAgentHandlers,
+  createConfigHandlers,
 } from './handlers/index.js';
 import type { SessionManager } from '../session/manager.js';
+import type { Config } from '../config/index.js';
 import type { ToolRegistry } from '../tools/registry.js';
 import type { ToolExecutor } from '../tools/executor.js';
 
@@ -34,6 +36,9 @@ export interface GatewayServerConfig {
   version?: string;
   auth?: AuthConfig;
   uiDir?: string;
+  config?: Config;
+  /** Optional callback for system.restart. Should trigger graceful shutdown + process restart. */
+  restart?: () => Promise<void>;
 }
 
 export class GatewayServer {
@@ -67,6 +72,7 @@ export class GatewayServer {
       getSessionCount: () => this.sessionBridge.listSessions().length,
       getToolCount: () => this.config.toolRegistry.list().length,
       getConnectionCount: () => this.sessionBridge.connectionCount,
+      restart: this.config.restart,
     });
 
     const sessionHandlers = createSessionHandlers({
@@ -82,6 +88,14 @@ export class GatewayServer {
       sessionBridge: this.sessionBridge,
     });
 
+    // Config handlers (only if config object is provided)
+    if (this.config.config) {
+      const configHandlers = createConfigHandlers({ config: this.config.config });
+      for (const [method, handler] of Object.entries(configHandlers)) {
+        this.router.register(method, handler);
+      }
+    }
+
     // Register all methods
     for (const [method, handler] of Object.entries(systemHandlers)) {
       this.router.register(method, handler);