Add task management: aggregated Tasks view (list + calendar) with inline due/priority, check off, set from row, and drag-to-reschedule (#62)

src/lib/components/Sidebar.svelte

@@ -150,6 +150,13 @@
 		onViewChanged();
 	}
 
+	function selectTasks() {
+		$viewMode = 'tasks';
+		$activeNotebook = null;
+		$activeTag = null;
+		onViewChanged();
+	}
+
 	function selectTrash() {
 		$viewMode = 'trash';
 		$activeNotebook = null;
@@ -511,6 +518,18 @@
 				<span>Quick Access</span>
 			</button>
 
+			<button
+				class="nav-item"
+				class:active={$viewMode === 'tasks'}
+				onclick={selectTasks}
+			>
+				<svg width="18" height="18" viewBox="0 0 24 24" fill="none" stroke="currentColor" stroke-width="2" stroke-linecap="round" stroke-linejoin="round">
+					<path d="M9 11l3 3L22 4" />
+					<path d="M21 12v7a2 2 0 01-2 2H5a2 2 0 01-2-2V5a2 2 0 012-2h11" />
+				</svg>
+				<span>Tasks</span>
+			</button>
+
 			<button
 				class="nav-item"
 				class:active={$viewMode === 'daily'}