feat: migrate backend logging from Winston to Pino with correlation IDs (refs #82)

- Replace Winston with Pino using API-compatible wrapper
- Add LOG_LEVEL env var support with validation and fallback
- Add correlation ID middleware (X-Request-Id from Traefik or UUID)
- Configure PostgreSQL logging env vars (POSTGRES_LOG_STATEMENT, POSTGRES_LOG_MIN_DURATION)
- Configure Redis loglevel via command args

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

backend/src/core/logging/logger.ts

@@ -1,24 +1,42 @@
 /**
- * @ai-summary Structured logging with Winston
- * @ai-context All features use this for consistent logging
+ * @ai-summary Structured logging with Pino (Winston-compatible wrapper)
+ * @ai-context All features use this for consistent logging. API maintains Winston compatibility.
  */
-import * as winston from 'winston';
+import pino from 'pino';
 
-export const logger = winston.createLogger({
-  level: 'info',
-  format: winston.format.combine(
-    winston.format.timestamp(),
-    winston.format.errors({ stack: true }),
-    winston.format.json()
-  ),
-  defaultMeta: {
-    service: 'motovaultpro-backend',
+type LogLevel = 'debug' | 'info' | 'warn' | 'error';
+const validLevels: LogLevel[] = ['debug', 'info', 'warn', 'error'];
+
+const rawLevel = (process.env.LOG_LEVEL?.toLowerCase() || 'info') as LogLevel;
+const level = validLevels.includes(rawLevel) ? rawLevel : 'info';
+
+if (process.env.LOG_LEVEL && rawLevel !== level) {
+  console.warn(`Invalid LOG_LEVEL "${process.env.LOG_LEVEL}", falling back to "info"`);
+}
+
+const pinoLogger = pino({
+  level,
+  formatters: {
+    level: (label) => ({ level: label }),
   },
-  transports: [
-    new winston.transports.Console({
-      format: winston.format.json(),
-    }),
-  ],
+  timestamp: pino.stdTimeFunctions.isoTime,
 });
 
-export default logger;
+// Wrapper maintains logger.info(msg, meta) API for backward compatibility
+export const logger = {
+  info: (msg: string, meta?: object) => pinoLogger.info(meta || {}, msg),
+  warn: (msg: string, meta?: object) => pinoLogger.warn(meta || {}, msg),
+  error: (msg: string, meta?: object) => pinoLogger.error(meta || {}, msg),
+  debug: (msg: string, meta?: object) => pinoLogger.debug(meta || {}, msg),
+  child: (bindings: object) => {
+    const childPino = pinoLogger.child(bindings);
+    return {
+      info: (msg: string, meta?: object) => childPino.info(meta || {}, msg),
+      warn: (msg: string, meta?: object) => childPino.warn(meta || {}, msg),
+      error: (msg: string, meta?: object) => childPino.error(meta || {}, msg),
+      debug: (msg: string, meta?: object) => childPino.debug(meta || {}, msg),
+    };
+  },
+};
+
+export default logger;

backend/src/core/plugins/logging.plugin.ts

@@ -1,20 +1,24 @@
 /**
- * @ai-summary Fastify request logging plugin
- * @ai-context Logs request/response details with timing
+ * @ai-summary Fastify request logging plugin with correlation IDs
+ * @ai-context Logs request/response details with timing and requestId
  */
 import { FastifyPluginAsync } from 'fastify';
 import fp from 'fastify-plugin';
+import { randomUUID } from 'crypto';
 import { logger } from '../logging/logger';
 
 const loggingPlugin: FastifyPluginAsync = async (fastify) => {
   fastify.addHook('onRequest', async (request) => {
     request.startTime = Date.now();
+    // Extract X-Request-Id from Traefik or generate new UUID
+    request.requestId = (request.headers['x-request-id'] as string) || randomUUID();
   });
 
   fastify.addHook('onResponse', async (request, reply) => {
     const duration = Date.now() - (request.startTime || Date.now());
-    
+
     logger.info('Request processed', {
+      requestId: request.requestId,
       method: request.method,
       path: request.url,
       status: reply.statusCode,
@@ -24,13 +28,13 @@ const loggingPlugin: FastifyPluginAsync = async (fastify) => {
   });
 };
 
-// Augment FastifyRequest to include startTime
 declare module 'fastify' {
   interface FastifyRequest {
     startTime?: number;
+    requestId?: string;
   }
 }
 
 export default fp(loggingPlugin, {
   name: 'logging-plugin'
-});
+});