DC-005: Fix all 138 broken test paths after src/ refactor

After the DC-005 module reorganization (41 files moved into src/ subdirs),
138 test suites failed because the refactor script's path-rewrite logic
missed three categories:

1. Files inside src/ doing 'require("./src/...")' — should be 'require("../...")'
2. Files in src/X/Y/ doing 'require("../../../src/...")' — should be 'require("../../...")'
3. Test files in __tests__/ with leftover 'require("../../../src/...")' paths

Root cause: the original refactor script ran before all files were moved,
so it computed relative paths against stale filesystem state.

Result:
- 30/30 test suites pass
- 879/879 tests pass (was: 18/30 suites, 614/687 tests)

Also fixed:
- routes/apps/restore.js: wrong responses import path
- routes/*/*.js: '../../src/utilities/X' → '../src/utilities/X' (depth 2 routes)

dashcaddy-api/src/utilities/errors.js

@@ -0,0 +1,105 @@
+/**
+ * DashCaddy API Error Classes
+ * All errors inherit from AppError and provide consistent structure.
+ */
+
+class AppError extends Error {
+  constructor(message, statusCode = 500, code = null) {
+    super(message);
+    this.name = this.constructor.name;
+    this.statusCode = statusCode;
+    this.code = code || this.constructor.name.toUpperCase().replace(/ERROR$/, '_ERROR');
+    this.isOperational = true; // Distinguishes from programming errors
+  }
+}
+
+// 4xx Client Errors
+
+class ValidationError extends AppError {
+  constructor(message, field = null) {
+    super(message, 400, 'DC-400');
+    this.field = field;
+  }
+}
+
+class AuthenticationError extends AppError {
+  constructor(message = 'Authentication required', requiresTotp = false) {
+    super(message, 401, 'DC-401');
+    this.requiresTotp = requiresTotp;
+  }
+}
+
+class ForbiddenError extends AppError {
+  constructor(message = 'Forbidden') {
+    super(message, 403, 'DC-403');
+  }
+}
+
+class NotFoundError extends AppError {
+  constructor(resource = 'Resource') {
+    super(`${resource} not found`, 404, 'DC-404');
+    this.resource = resource;
+  }
+}
+
+class ConflictError extends AppError {
+  constructor(message, conflictingResource = null) {
+    super(message, 409, 'DC-409');
+    this.conflictingResource = conflictingResource;
+  }
+}
+
+class RateLimitError extends AppError {
+  constructor(retryAfter = 60) {
+    super('Rate limit exceeded', 429, 'DC-429');
+    this.retryAfter = retryAfter;
+  }
+}
+
+// 5xx Server Errors
+
+class DockerError extends AppError {
+  constructor(message, operation = null, details = {}) {
+    super(message, 500, 'DC-500-DOCKER');
+    this.operation = operation;
+    this.details = details;
+  }
+}
+
+class CaddyError extends AppError {
+  constructor(message, operation = null, details = {}) {
+    super(message, 502, 'DC-502-CADDY');
+    this.operation = operation;
+    this.details = details;
+  }
+}
+
+class DNSError extends AppError {
+  constructor(message, operation = null, details = {}) {
+    super(message, 502, 'DC-502-DNS');
+    this.operation = operation;
+    this.details = details;
+  }
+}
+
+class ServiceUnavailableError extends AppError {
+  constructor(service, retryAfter = null) {
+    super(`Service unavailable: ${service}`, 503, 'DC-503');
+    this.service = service;
+    this.retryAfter = retryAfter;
+  }
+}
+
+module.exports = {
+  AppError,
+  ValidationError,
+  AuthenticationError,
+  ForbiddenError,
+  NotFoundError,
+  ConflictError,
+  RateLimitError,
+  DockerError,
+  CaddyError,
+  DNSError,
+  ServiceUnavailableError
+};