feat: Notion sidebar complete — 7 sections, nav icons, auto-update title

- Sidebar: 7 collapsible sections (Meetings, Recents, Favorites, Agents, Shared, Private, Notion apps)
- Nav icon row: Home with text + icon, Chat/Inbox/Search icon-only, collapse on right
- Notion apps: Library, My Tasks, Trash, Help
- Footer: New chat Ctrl+O + New page buttons
- Auto-update: sidebar items reflect title changes immediately on save
- CSS: nav-icon-btn, home-btn, collapse-btn, empty-hint, outline none

static/css/app.css

@@ -221,6 +221,31 @@ input, select, textarea { font-family: inherit; color: inherit; }
   flex-shrink: 0;
 }
 
+/* Navigation icon row (Notion top bar) */
+.sidebar-nav-row {
+  display: flex; align-items: center; gap: 3px;
+  padding: 6px 6px; margin: 0 2px;
+}
+.nav-icon-btn {
+  display: flex; align-items: center; gap: 8px;
+  padding: 6px; border-radius: 6px;
+  color: var(--text-secondary); transition: background 0.15s, color 0.15s;
+}
+.nav-icon-btn:hover { background: var(--bg-hover); color: var(--text-primary); }
+.nav-icon-btn.active { background: var(--bg-active); color: var(--text-primary); }
+/* Home button: icon + text */
+.nav-icon-btn.home-btn {
+  padding: 6px 8px; gap: 8px;
+  font-size: 14px; font-weight: 500;
+}
+/* Collapse button on the right */
+.nav-icon-btn.collapse-btn { margin-left: auto; }
+
+/* Empty hint */
+.sidebar-item.empty-hint { color: var(--text-dim); font-size: 12px; cursor: default; }
+.sidebar-item.empty-hint:hover { background: none; }
+.sidebar-item.empty-hint .page-name { font-size: 12px; }
+
 /* Sections */
 .sidebar-section {
   padding: var(--space-xs) var(--space-md);