feat(ui): unify header and implement navigation drawer (Task 17)

- Redesign top header into clean, uncluttered layout with hamburger drawer trigger, clickable logo, central SRS focus badge, theme toggle and profile avatar
- Implement unified responsive Navigation Drawer for both desktop and mobile with touch swipe-to-dismiss, backdrop blur, keyboard Esc support and background scroll lock
- Streamline mobile bottom tab bar to 4 core actions (Dictionary, SRS, Reader, Menu) with Menu opening the unified drawer
- Synchronize real-time SRS due badges and dictionary word statistics between header, bottom tabs, and drawer
- Eliminate obsolete separate mobile-menu-modal in favor of unified drawer
- Bump Service Worker cache version to notes-v5.7

app/static/js/modules/dictionary.js

@@ -96,6 +96,7 @@ export function initDictionary() {
     const moveColConfirmBtn = document.getElementById('move-col-confirm-btn');
 
     const exportOpenBtn = document.getElementById('export-open-btn');
+    const drawerNavExport = document.getElementById('drawer-nav-export');
     const exportModal = document.getElementById('export-modal');
     const closeExportModalBtn = document.getElementById('close-export-modal-btn');
     const exportCancelBtn = document.getElementById('export-cancel-btn');
@@ -556,6 +557,9 @@ export function initDictionary() {
     if (exportOpenBtn) {
         exportOpenBtn.addEventListener('click', () => openModal(exportModal));
     }
+    if (drawerNavExport) {
+        drawerNavExport.addEventListener('click', () => openModal(exportModal));
+    }
     closeExportModalBtn.addEventListener('click', () => closeModal(exportModal));
     exportCancelBtn.addEventListener('click', () => closeModal(exportModal));
 
@@ -687,12 +691,22 @@ export function initDictionary() {
             if (stats) {
                 const due = stats.due_cards || 0;
                 const srsBadge = document.getElementById('srs-badge');
-                if (srsBadge) srsBadge.textContent = due;
+                if (srsBadge) {
+                    srsBadge.textContent = due;
+                    srsBadge.style.display = due > 0 ? 'inline-block' : 'none';
+                }
                 const tabSrsBadge = document.getElementById('tab-srs-badge');
                 if (tabSrsBadge) {
                     tabSrsBadge.textContent = due;
                     tabSrsBadge.classList.toggle('hidden', due === 0);
                 }
+                const drawerSrsBadge = document.getElementById('drawer-srs-badge');
+                if (drawerSrsBadge) {
+                    drawerSrsBadge.textContent = due;
+                    drawerSrsBadge.classList.toggle('hidden', due === 0);
+                }
+                const drawerStatDue = document.getElementById('drawer-stat-due');
+                if (drawerStatDue) drawerStatDue.textContent = due;
             }
         } catch (e) {}
     }