feat: add web UI, query engine, session management, and 20 E2E tests

- Web UI: login, dashboard, links CRUD, collections, API keys, admin pages
- Query engine: AND/OR/XOR with field filters, tag search, preview endpoint
- Session management: token expiry detection, 401 interceptor, expiry banner
- Links search: tags included, multi-word AND, query mode with set operations
- Collections: static/dynamic, query builder with preview, public tree view
- Save as Collection: convert search results (static) or query (dynamic)
- Dashboard stats: resilient loading with allSettled pattern
- Login page: redesigned with public collections tree view
- Bug fix: query executor None fields crash (notes/description/url/title)
- E2E tests: 20 Playwright tests covering all critical user flows
- All 104 tests passing (84 unit/integration + 20 E2E)

LinkSyncServer/static/js/dashboard.js

@@ -5,6 +5,12 @@ document.addEventListener('DOMContentLoaded', async function() {
         return;
     }
 
+    const token = localStorage.getItem('token');
+    if (token && LinkSync.isTokenExpired(token)) {
+        LinkSync.logout();
+        return;
+    }
+
     document.getElementById('current-user').textContent = user.username;
 
     if (user.role === 'admin') {
@@ -12,16 +18,28 @@ document.addEventListener('DOMContentLoaded', async function() {
     }
 
     try {
-        const [links, collections, keys] = await Promise.all([
+        const [linksResult, collectionsResult, keysResult] = await Promise.allSettled([
             LinkSync.getLinks({ limit: 1 }),
             LinkSync.getCollections(),
             LinkSync.getApiKeys(),
         ]);
 
+        const links = linksResult.status === 'fulfilled' ? linksResult.value : [];
+        const collections = collectionsResult.status === 'fulfilled' ? collectionsResult.value : [];
+        const keys = keysResult.status === 'fulfilled' ? keysResult.value : [];
+
         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);
     }
+
+    const expirySeconds = LinkSync.getTokenExpirySeconds(token);
+    if (expirySeconds > 0 && expirySeconds < 120) {
+        const warning = document.createElement('div');
+        warning.className = 'info-message';
+        warning.textContent = `Session expires in ${Math.ceil(expirySeconds / 60)} minute${expirySeconds > 60 ? 's' : ''}. Save your work.`;
+        document.querySelector('.dashboard-header').prepend(warning);
+    }
 });