feat: implement Winston logging service

- Add LogEntry interface for structured log data
- Create LoggerService with Winston integration
- Support for console and file transports (app.log, error.log)
- Implement UI log notification callbacks
- Provide info, warn, error, and debug logging methods
- Configure log rotation (10MB max, 5 files retained)

Co-Authored-By: Claude Sonnet 4.5 <noreply@anthropic.com>

src/main/models/logger.types.ts

@@ -0,0 +1,6 @@
+export interface LogEntry {
+  timestamp: string;
+  level: string;
+  message: string;
+  details?: any;
+}

src/main/services/logger.service.ts

@@ -0,0 +1,94 @@
+import winston from 'winston';
+import path from 'path';
+import { app } from 'electron';
+import { LogEntry } from '../models/logger.types';
+
+export class LoggerService {
+  private static instance: winston.Logger | null = null;
+  private static uiLogCallbacks: Set<(logEntry: LogEntry) => void> = new Set();
+
+  static initialize(): winston.Logger {
+    if (this.instance) {
+      return this.instance;
+    }
+
+    const logDir = path.join(app.getPath('userData'), 'logs');
+
+    this.instance = winston.createLogger({
+      level: 'info',
+      format: winston.format.combine(
+        winston.format.timestamp({ format: 'YYYY-MM-DD HH:mm:ss' }),
+        winston.format.errors({ stack: true }),
+        winston.format.printf(({ level, message, timestamp, stack }) => {
+          if (stack) {
+            return `[${timestamp}] [${level.toUpperCase()}] ${message}\n${stack}`;
+          }
+          return `[${timestamp}] [${level.toUpperCase()}] ${message}`;
+        })
+      ),
+      transports: [
+        new winston.transports.Console({
+          format: winston.format.combine(
+            winston.format.colorize(),
+            winston.format.simple()
+          ),
+        }),
+        new winston.transports.File({
+          filename: path.join(logDir, 'app.log'),
+          maxsize: 10 * 1024 * 1024,
+          maxFiles: 5,
+        }),
+        new winston.transports.File({
+          filename: path.join(logDir, 'error.log'),
+          level: 'error',
+          maxsize: 10 * 1024 * 1024,
+          maxFiles: 5,
+        }),
+      ],
+    });
+
+    return this.instance;
+  }
+
+  static onUILog(callback: (logEntry: LogEntry) => void): () => void {
+    this.uiLogCallbacks.add(callback);
+    return () => {
+      this.uiLogCallbacks.delete(callback);
+    };
+  }
+
+  private static notifyUI(level: string, message: string, details?: any): void {
+    const logEntry: LogEntry = {
+      timestamp: new Date().toISOString(),
+      level,
+      message,
+      details,
+    };
+
+    this.uiLogCallbacks.forEach((callback) => callback(logEntry));
+  }
+
+  static info(message: string, details?: any): void {
+    if (!this.instance) this.initialize();
+    this.instance!.info(message, details);
+    this.notifyUI('info', message, details);
+  }
+
+  static warn(message: string, details?: any): void {
+    if (!this.instance) this.initialize();
+    this.instance!.warning(message, details);
+    this.notifyUI('warn', message, details);
+  }
+
+  static error(message: string, details?: any): void {
+    if (!this.instance) this.initialize();
+    this.instance!.error(message, details);
+    this.notifyUI('error', message, details);
+  }
+
+  static debug(message: string, details?: any): void {
+    if (!this.instance) this.initialize();
+    this.instance!.debug(message, details);
+    this.notifyUI('debug', message, details);
+  }
+}