feat(time-tracking) : add calendar page, timer sidebar, and all UI components

- SidebarTimer widget with play/stop button
- TimeEntryBlock with drag-to-move and resize
- TimeEntryDrawer for create/edit entries
- TimeEntryContextMenu for copy/paste/delete
- TimeTrackingCalendar grid with week/day view
- Time tracking page with filters and navigation
- Sidebar link and timer integration in layout
- TaskCard play button connected to timer store

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

frontend/components/TaskCard.vue

@@ -10,7 +10,7 @@
             <h4 class="text-sm font-semibold text-neutral-900">{{ task.title }}</h4>
             <button
                 class="shrink-0 text-neutral-400 hover:text-primary-500"
-                @click.stop
+                @click.stop="onPlay"
             >
                 <Icon name="mdi:play-circle-outline" size="20" />
             </button>
@@ -60,6 +60,12 @@ const emit = defineEmits<{
     (e: 'click'): void
 }>()
 
+const timerStore = useTimerStore()
+
+function onPlay() {
+    timerStore.startFromTask(props.task)
+}
+
 function onDragStart(event: DragEvent) {
     event.dataTransfer!.effectAllowed = 'move'
     event.dataTransfer!.setData('text/plain', String(props.task.id))