feat(gateway): enhance gateway process management with auto-reconnection

Improve Gateway lifecycle management with the following features:

- Add exponential backoff reconnection (1s-30s delay, max 10 attempts)
- Add health check monitoring every 30 seconds
- Add proper restart method with graceful shutdown
- Handle server-initiated notifications (channel status, chat messages)
- Add 'reconnecting' state for better UI feedback
- Enhance IPC handlers with isConnected and health check endpoints
- Update preload script with new event channels
- Improve type safety and error handling throughout

Also fixes several TypeScript errors and unused variable warnings.

src/types/gateway.ts

@@ -7,12 +7,14 @@
  * Gateway connection status
  */
 export interface GatewayStatus {
-  state: 'stopped' | 'starting' | 'running' | 'error';
+  state: 'stopped' | 'starting' | 'running' | 'error' | 'reconnecting';
   port: number;
   pid?: number;
   uptime?: number;
   error?: string;
   connectedAt?: number;
+  version?: string;
+  reconnectAttempts?: number;
 }
 
 /**
@@ -23,3 +25,34 @@ export interface GatewayRpcResponse<T = unknown> {
   result?: T;
   error?: string;
 }
+
+/**
+ * Gateway health check response
+ */
+export interface GatewayHealth {
+  ok: boolean;
+  error?: string;
+  uptime?: number;
+  version?: string;
+}
+
+/**
+ * Gateway notification (server-initiated event)
+ */
+export interface GatewayNotification {
+  method: string;
+  params?: unknown;
+}
+
+/**
+ * Provider configuration
+ */
+export interface ProviderConfig {
+  id: string;
+  name: string;
+  type: 'openai' | 'anthropic' | 'ollama' | 'custom';
+  apiKey?: string;
+  baseUrl?: string;
+  model?: string;
+  enabled: boolean;
+}