Add greeting and countdown timer to TV dashboard before session starts

Shows "Good Morning! Ready to start school?" placeholder when a session
is active but no block has been selected, along with a live countdown
to the first scheduled block's start time.

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

frontend/src/views/TVView.vue

@@ -26,7 +26,15 @@
     <!-- Active session -->
     <div v-else class="tv-main">
       <!-- Left: timer -->
-      <div class="tv-timer-col" v-if="scheduleStore.currentBlock">
+      <div class="tv-timer-col tv-greeting-col" v-if="!scheduleStore.currentBlock">
+        <div class="tv-greeting">Good Morning!</div>
+        <div class="tv-greeting-sub">Ready to start school?</div>
+        <div v-if="firstBlockCountdown !== null" class="tv-countdown-wrap">
+          <div class="tv-countdown-label">First block starts in</div>
+          <div class="tv-countdown">{{ firstBlockCountdown }}</div>
+        </div>
+      </div>
+      <div class="tv-timer-col" v-else>
         <div class="tv-subject-badge" :style="{ background: currentSubjectColor }">
           {{ currentSubjectIcon }} {{ currentSubjectName }}
         </div>
@@ -129,6 +137,23 @@ const dayProgressPercent = computed(() => {
   return Math.max(0, Math.min(100, Math.round((nowMin - start) / (end - start) * 100)))
 })
 
+// Countdown to first block
+const firstBlockCountdown = computed(() => {
+  const first = scheduleStore.blocks[0]
+  if (!first?.time_start) return null
+  const [h, m, s] = first.time_start.split(':').map(Number)
+  const target = new Date(now.value)
+  target.setHours(h, m, s || 0, 0)
+  const diffMs = target - now.value
+  if (diffMs <= 0) return null
+  const totalSec = Math.floor(diffMs / 1000)
+  const hours = Math.floor(totalSec / 3600)
+  const mins = Math.floor((totalSec % 3600) / 60)
+  const secs = totalSec % 60
+  if (hours > 0) return `${hours}:${String(mins).padStart(2, '0')}:${String(secs).padStart(2, '0')}`
+  return `${String(mins).padStart(2, '0')}:${String(secs).padStart(2, '0')}`
+})
+
 // Subject display helpers
 const currentSubjectColor = computed(() => {
   const block = scheduleStore.currentBlock
@@ -228,6 +253,47 @@ onMounted(async () => {
   text-align: center;
 }
 
+.tv-greeting-col {
+  justify-content: center;
+  gap: 1rem;
+}
+
+.tv-greeting {
+  font-size: 3rem;
+  font-weight: 700;
+  color: #818cf8;
+  text-align: center;
+}
+
+.tv-greeting-sub {
+  font-size: 1.6rem;
+  color: #64748b;
+  text-align: center;
+}
+
+.tv-countdown-wrap {
+  margin-top: 1.5rem;
+  display: flex;
+  flex-direction: column;
+  align-items: center;
+  gap: 0.4rem;
+}
+
+.tv-countdown-label {
+  font-size: 1rem;
+  text-transform: uppercase;
+  letter-spacing: 0.08em;
+  color: #475569;
+}
+
+.tv-countdown {
+  font-size: 4rem;
+  font-weight: 300;
+  font-variant-numeric: tabular-nums;
+  color: #c7d2fe;
+  letter-spacing: 0.05em;
+}
+
 .tv-block-notes {
   font-size: 1rem;
   color: #94a3b8;