feat(08-01): Health monitoring & logging infrastructure

- Set up Winston structured logging with console and file outputs
- Create GET /api/health endpoint with uptime, database status, response times
- Add request logging middleware (method, path, statusCode, duration)
- Create health monitoring module with database connectivity checks
- Log all HTTP requests with timing information
- Log auth events (login, register) and data modifications
- Replace console.log/error with structured logger calls
- Update backend README with logging configuration documentation
- Add tests for health endpoint and logging middleware
- Logs directory: logs/combined.log and logs/error.log

Deliverables met:
✓ Structured logging (Winston) integrated
✓ Enhanced health endpoint with uptime & database info
✓ Request logging middleware attached to all routes
✓ Comprehensive logging documentation in README.md
✓ Tests passing for health and logging functionality
✓ All critical operations logged with context

backend/src/utils/health.js

@@ -0,0 +1,58 @@
+const { Pool } = require('pg');
+const logger = require('./logger');
+
+/**
+ * Health Monitoring Module
+ * Tracks application health metrics including uptime and database connectivity
+ */
+
+const startTime = Date.now();
+
+/**
+ * Get application health status
+ * @returns {Object} Health status object with status, uptime, and timestamp
+ */
+async function getHealthStatus(pool) {
+  try {
+    // Check database connectivity
+    const dbHealthStart = Date.now();
+    const dbResult = await pool.query('SELECT NOW()');
+    const dbHealthDuration = Date.now() - dbHealthStart;
+    
+    const dbHealthy = dbResult.rows.length > 0;
+
+    return {
+      status: dbHealthy ? 'healthy' : 'degraded',
+      uptime: Math.floor((Date.now() - startTime) / 1000), // uptime in seconds
+      timestamp: new Date().toISOString(),
+      database: {
+        connected: dbHealthy,
+        responseTime: `${dbHealthDuration}ms`
+      }
+    };
+  } catch (err) {
+    logger.error('Health check failed', { error: err.message });
+    return {
+      status: 'unhealthy',
+      uptime: Math.floor((Date.now() - startTime) / 1000),
+      timestamp: new Date().toISOString(),
+      database: {
+        connected: false,
+        error: err.message
+      }
+    };
+  }
+}
+
+/**
+ * Get uptime in seconds since application start
+ * @returns {number} Uptime in seconds
+ */
+function getUptime() {
+  return Math.floor((Date.now() - startTime) / 1000);
+}
+
+module.exports = {
+  getHealthStatus,
+  getUptime
+};