feat: Add comprehensive settings modal and backup/restore tests

E2E Tests (tests/frontend/e2e/settings_modal.spec.js):
- Modal open/close: button, overlay, Escape (5 tests)
- Configuration sections: all sections display (5 tests)
- Load configuration: directory, count, scheduler, status (4 tests)
- Edit fields: name, directory, scheduler, interval (6 tests)
- Save configuration: main, scheduler, feedback (4 tests)
- Reset configuration to original values (2 tests)
- Browse directory functionality (2 tests)
- Connection test and status update (2 tests)
- Scheduler status: next/last rescan, running (3 tests)
- Accessibility: labels, keyboard nav, focus trap (4 tests)
- Edge cases: rapid changes, long inputs, multiple opens (5 tests)
- Theme integration: respect theme, toggle (2 tests)
Total: 44 E2E tests

Integration Tests (tests/integration/test_config_backup_restore.py):
- Backup creation: default/custom name, auth, file creation (6 tests)
- Backup listing: array, metadata, recent, auth (5 tests)
- Backup restoration: valid, nonexistent, pre-backup, auth (6 tests)
- Backup deletion: existing, removes file/list, auth (5 tests)
- Complete workflows: full cycle, multiple cycles (3 tests)
- Edge cases: invalid names, concurrent ops, long names (4 tests)
Total: 29 integration tests

Updated instructions.md marking settings modal tests complete

tests/frontend/e2e/setup_page.spec.js

@@ -5,7 +5,7 @@
  * Tests form validation, password strength, submission, and all configuration sections
  */
 
-import { test, expect } from '@playwright/test';
+import { expect, test } from '@playwright/test';
 
 test.describe('Setup Page - Initial Load', () => {
     test('should load setup page when not configured', async ({ page }) => {