feat: integrate all 10 skills into homelab-topology

- Added api-security-hardening (helmet, rate limits)
- Added nodejs-backend-patterns (error handling)
- Added observability-monitoring (pino logging)
- Added websocket-engineer (socket.io real-time updates)
- Added docker (Multi-stage build, compose)
- Added vitest (testing configuration and store tests)
- Added data-visualizer (MetricsBar and HostChart)
- Added infrastructure-monitoring/proxmox-admin/network-engineer types
- Fixed UI accessibility and styling
- Cleaned up node_modules tracking

server/middleware/errorHandler.ts

@@ -0,0 +1,42 @@
+import { Request, Response, NextFunction } from 'express';
+import { AppError, ValidationError } from '../errors';
+import { logger } from './requestLogger';
+
+/**
+ * Global error handler middleware.
+ * Catches all errors, logs unexpected ones with Pino, and returns safe JSON responses.
+ * Must be registered AFTER all routes.
+ */
+export const errorHandler = (
+    err: Error,
+    req: Request,
+    res: Response,
+    _next: NextFunction
+) => {
+    if (err instanceof AppError) {
+        return res.status(err.statusCode).json({
+            status: 'error',
+            message: err.message,
+            ...(err instanceof ValidationError && err.errors ? { errors: err.errors } : {}),
+        });
+    }
+
+    // Log unexpected errors
+    logger.error({
+        error: err.message,
+        stack: err.stack,
+        url: req.url,
+        method: req.method,
+    });
+
+    // Don't leak error details in production
+    const message =
+        process.env.NODE_ENV === 'production'
+            ? 'Internal server error'
+            : err.message;
+
+    res.status(500).json({
+        status: 'error',
+        message,
+    });
+};