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/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'
-});
+});