feat: add web UI with login, CRUD, admin, and API key management

- Add login page with JWT authentication
- Add dashboard with stats and quick actions
- Add links management page (full CRUD with search)
- Add collections management page
- Add API key management page with copy-to-clipboard
- Add admin user management page (admin only)
- Fix UUID type mismatches across all endpoints
- Add updated_at column to api_keys and audit_log in schema.sql
- Fix DB_PASSWORD default in docker-compose.yml
- Add PyJWT to requirements.txt
- Fix API docs URL (/docs instead of /api/docs)
- Improve JS error handling (show actual messages)
- Rewrite conftest.py with proper DB lifecycle management
- Add 42 new integration tests (84 total, all passing)
  - test_admin.py: 15 tests for admin endpoints
  - test_auth_extended.py: 9 tests for API key CRUD
  - test_tags.py: 12 tests for tag endpoints
  - test_sync.py: 6 tests for sync endpoints

LinkSyncServer/static/js/dashboard.js

@@ -0,0 +1,27 @@
+document.addEventListener('DOMContentLoaded', async function() {
+    const user = JSON.parse(localStorage.getItem('user') || 'null');
+    if (!user) {
+        window.location.href = '/login';
+        return;
+    }
+
+    document.getElementById('current-user').textContent = user.username;
+
+    if (user.role === 'admin') {
+        document.getElementById('admin-section').style.display = '';
+    }
+
+    try {
+        const [links, collections, keys] = await Promise.all([
+            LinkSync.getLinks({ limit: 1 }),
+            LinkSync.getCollections(),
+            LinkSync.getApiKeys(),
+        ]);
+
+        document.getElementById('link-count').textContent = Array.isArray(links) ? links.length : 0;
+        document.getElementById('collection-count').textContent = Array.isArray(collections) ? collections.length : 0;
+        document.getElementById('api-key-count').textContent = Array.isArray(keys) ? keys.length : 0;
+    } catch (err) {
+        console.error('Failed to load stats:', err);
+    }
+});