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/errors.ts

@@ -0,0 +1,36 @@
+/**
+ * Custom Error Classes for Homelab Topology API
+ * 
+ * Structured error hierarchy following nodejs-backend-patterns skill.
+ * All operational errors extend AppError with appropriate HTTP status codes.
+ */
+
+export class AppError extends Error {
+    constructor(
+        public message: string,
+        public statusCode: number = 500,
+        public isOperational: boolean = true
+    ) {
+        super(message);
+        Object.setPrototypeOf(this, AppError.prototype);
+        Error.captureStackTrace(this, this.constructor);
+    }
+}
+
+export class NotFoundError extends AppError {
+    constructor(message: string = 'Resource not found') {
+        super(message, 404);
+    }
+}
+
+export class ValidationError extends AppError {
+    constructor(message: string, public errors?: Array<{ field: string; message: string }>) {
+        super(message, 400);
+    }
+}
+
+export class ServiceUnavailableError extends AppError {
+    constructor(message: string = 'Service temporarily unavailable') {
+        super(message, 503);
+    }
+}