feat: Reinitialize frontend with SvelteKit and TypeScript

- Delete old Vite+Svelte frontend
- Initialize new SvelteKit project with TypeScript
- Configure Tailwind CSS v4 + DaisyUI
- Implement JWT authentication with auto-refresh
- Create login page with form validation (Zod)
- Add protected route guards
- Update Docker configuration for single-stage build
- Add E2E tests with Playwright (6/11 passing)
- Fix Svelte 5 reactivity with $state() runes

Known issues:
- 5 E2E tests failing (timing/async issues)
- Token refresh implementation needs debugging
- Validation error display timing

frontend/node_modules/happy-dom/lib/nodes/child-node/NonDocumentChildNodeUtility.js

@@ -0,0 +1,34 @@
+import NodeTypeEnum from '../node/NodeTypeEnum.js';
+import * as PropertySymbol from '../../PropertySymbol.js';
+/**
+ * Non Document Child node utility.
+ */
+export default class NonDocumentChildNodeUtility {
+    /**
+     * Previous element sibling.
+     *
+     * @param childNode Child node.
+     * @returns Element.
+     */
+    static previousElementSibling(childNode) {
+        let sibling = childNode.previousSibling;
+        while (sibling && sibling[PropertySymbol.nodeType] !== NodeTypeEnum.elementNode) {
+            sibling = sibling.previousSibling;
+        }
+        return sibling;
+    }
+    /**
+     * Next element sibling.
+     *
+     * @param childNode Child node.
+     * @returns Element.
+     */
+    static nextElementSibling(childNode) {
+        let sibling = childNode.nextSibling;
+        while (sibling && sibling[PropertySymbol.nodeType] !== NodeTypeEnum.elementNode) {
+            sibling = sibling.nextSibling;
+        }
+        return sibling;
+    }
+}
+//# sourceMappingURL=NonDocumentChildNodeUtility.js.map