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/layouts/default.vue

@@ -63,6 +63,12 @@
                         label="Clients"
                         :collapsed="ui.sidebarCollapsed"
                     />
+                    <SidebarLink
+                        to="/time-tracking"
+                        icon="mdi:clock-outline"
+                        label="Suivi de temps"
+                        :collapsed="ui.sidebarCollapsed"
+                    />
                     <SidebarLink
                         to="/admin"
                         icon="mdi:cog-outline"
@@ -71,6 +77,10 @@
                     />
                 </nav>
 
+                <div class="px-4 py-3 border-t border-secondary-500">
+                    <SidebarTimer :collapsed="ui.sidebarCollapsed" />
+                </div>
+
                 <div class="flex flex-col gap-2 items-center p-4">
                     <p v-if="!ui.sidebarCollapsed" class="font-bold">v {{ version }}</p>
                     <button
@@ -109,6 +119,12 @@ const currentProjectId = computed(() => {
     return match ? match[1] : null
 })
 
+const timerStore = useTimerStore()
+
+onMounted(() => {
+    timerStore.fetchActive()
+})
+
 const handleLogout = async () => {
     await auth.logout()
     await navigateTo('/login')