Fix timer reset on refresh and sync between dashboard and TV view

- Backend computes block_elapsed_seconds server-side from timer_events
- Store tracks blockStartedAt (ms) + blockElapsedOffset (seconds) instead
  of a client-side counter; updated correctly on start/pause/resume/end
- TimerDisplay derives elapsed from store props so both views always agree
- Add compact timer display to dashboard session card
- Add isPaused/pause-resume logic to dashboard Pause/Resume buttons

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

frontend/src/views/DashboardView.vue

@@ -21,13 +21,27 @@
               <span>{{ scheduleStore.progressPercent }}% complete</span>
             </div>
             <ProgressBar :percent="scheduleStore.progressPercent" />
+            <div v-if="scheduleStore.currentBlock" class="current-block-timer">
+              <TimerDisplay
+                compact
+                :block="scheduleStore.currentBlock"
+                :session="scheduleStore.session"
+                :is-paused="scheduleStore.isPaused"
+                :block-started-at="scheduleStore.blockStartedAt"
+                :block-elapsed-offset="scheduleStore.blockElapsedOffset"
+              />
+            </div>
             <div class="session-actions">
               <button
                 class="btn-sm"
-                v-if="scheduleStore.session.current_block_id"
+                v-if="scheduleStore.session.current_block_id && !scheduleStore.isPaused"
                 @click="sendAction('pause')"
               >Pause</button>
-              <button class="btn-sm" @click="sendAction('start')">Resume</button>
+              <button
+                class="btn-sm"
+                v-if="scheduleStore.isPaused"
+                @click="sendAction('resume')"
+              >Resume</button>
               <button class="btn-sm btn-danger" @click="sendAction('complete')">End Day</button>
             </div>
           </div>
@@ -96,6 +110,7 @@ import NavBar from '@/components/NavBar.vue'
 import ChildSelector from '@/components/ChildSelector.vue'
 import ProgressBar from '@/components/ProgressBar.vue'
 import ScheduleBlock from '@/components/ScheduleBlock.vue'
+import TimerDisplay from '@/components/TimerDisplay.vue'
 
 const childrenStore = useChildrenStore()
 const scheduleStore = useScheduleStore()
@@ -135,6 +150,8 @@ async function sendAction(type) {
 
 function selectBlock(block) {
   if (!scheduleStore.session) return
+  scheduleStore.session.current_block_id = block.id
+  scheduleStore.isPaused = false
   scheduleStore.sendTimerAction(scheduleStore.session.id, 'start', block.id)
 }
 
@@ -189,6 +206,7 @@ h1 { font-size: 1.75rem; font-weight: 700; }
   font-weight: 600;
 }
 
+.current-block-timer { display: flex; justify-content: center; margin: 1rem 0; }
 .session-actions { display: flex; gap: 0.5rem; margin-top: 1rem; flex-wrap: wrap; }
 
 .btn-sm {