Add per-block agenda overrides for daily sessions

- Add 📝 Agenda button to each block in Today's Schedule on the Dashboard
- Dialog allows setting a free-text activity/note for that block for the current day
- Agenda replaces subject options in the TV center panel while set; clears on session end
- Backend: new SessionBlockAgenda model, PUT /api/sessions/{id}/blocks/{block_id}/agenda
- Agendas included in dashboard snapshot and session_update WS broadcast
- New agenda_update WS event keeps TV in sync live when agenda is saved or cleared
- Update README with feature description, project structure, and WS event table

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

frontend/src/views/DashboardView.vue

@@ -183,21 +183,50 @@
             No blocks loaded.
           </div>
           <div class="block-list" v-else>
-            <ScheduleBlock
-              v-for="block in scheduleStore.blocks"
-              :key="block.id"
-              :block="block"
-              :is-current="block.id === scheduleStore.session?.current_block_id"
-              :is-completed="scheduleStore.completedBlockIds.includes(block.id)"
-              :elapsed-seconds="blockElapsed(block)"
-              @click="selectBlock(block)"
-            />
+            <div v-for="block in scheduleStore.blocks" :key="block.id" class="block-row-wrap">
+              <ScheduleBlock
+                :block="block"
+                :is-current="block.id === scheduleStore.session?.current_block_id"
+                :is-completed="scheduleStore.completedBlockIds.includes(block.id)"
+                :elapsed-seconds="blockElapsed(block)"
+                @click="selectBlock(block)"
+              />
+              <button
+                class="agenda-btn"
+                :class="{ 'agenda-btn-set': scheduleStore.blockAgendas[String(block.id)] }"
+                @click.stop="openAgendaDialog(block)"
+                title="Set agenda for this block"
+              >📝</button>
+            </div>
           </div>
         </div>
         </div><!-- end bottom-row -->
 
       </div>
 
+      <!-- Agenda dialog -->
+      <div class="dialog-overlay" v-if="agendaDialog.open" @click.self="closeAgendaDialog">
+        <div class="dialog">
+          <h2>Block Agenda</h2>
+          <p class="dialog-hint">{{ agendaDialog.blockLabel }}</p>
+          <div class="field">
+            <label>Today's activity or note</label>
+            <textarea
+              v-model="agendaDialog.text"
+              class="agenda-textarea"
+              placeholder="e.g. Chapter 5 reading, worksheet page 12..."
+              rows="4"
+              @keydown.ctrl.enter="saveAgenda"
+            ></textarea>
+          </div>
+          <div class="dialog-actions">
+            <button class="btn-sm btn-danger" v-if="agendaDialog.existing" @click="clearAgenda">Clear</button>
+            <button class="btn-sm" @click="closeAgendaDialog">Cancel</button>
+            <button class="btn-primary" @click="saveAgenda">Save</button>
+          </div>
+        </div>
+      </div>
+
       <!-- Start session dialog -->
       <div class="dialog-overlay" v-if="showStartDialog" @click.self="showStartDialog = false">
         <div class="dialog">
@@ -370,6 +399,38 @@ const estimatedFinishTime = computed(() => {
   return `${hour}:${String(finish.getMinutes()).padStart(2, '0')} ${period}`
 })
 
+// Agenda dialog
+const agendaDialog = ref({ open: false, blockId: null, blockLabel: '', text: '', existing: false })
+
+function openAgendaDialog(block) {
+  if (!scheduleStore.session) return
+  const label = block.label || block.subject?.name || 'Block'
+  const existing = scheduleStore.blockAgendas[String(block.id)] || ''
+  agendaDialog.value = { open: true, blockId: block.id, blockLabel: label, text: existing, existing: !!existing }
+}
+
+function closeAgendaDialog() {
+  agendaDialog.value = { open: false, blockId: null, blockLabel: '', text: '', existing: false }
+}
+
+async function saveAgenda() {
+  if (!scheduleStore.session || agendaDialog.value.blockId === null) return
+  await api.put(
+    `/api/sessions/${scheduleStore.session.id}/blocks/${agendaDialog.value.blockId}/agenda`,
+    { text: agendaDialog.value.text }
+  )
+  closeAgendaDialog()
+}
+
+async function clearAgenda() {
+  if (!scheduleStore.session || agendaDialog.value.blockId === null) return
+  await api.put(
+    `/api/sessions/${scheduleStore.session.id}/blocks/${agendaDialog.value.blockId}/agenda`,
+    { text: '' }
+  )
+  closeAgendaDialog()
+}
+
 async function toggleRulesOverlay() {
   if (!activeChild.value) return
   const endpoint = scheduleStore.showRulesOverlay
@@ -529,6 +590,53 @@ h1 { font-size: 1.75rem; font-weight: 700; }
 
 .block-list { display: flex; flex-direction: column; gap: 0.5rem; }
 
+.block-row-wrap {
+  display: flex;
+  align-items: center;
+  gap: 0.5rem;
+}
+.block-row-wrap > :first-child { flex: 1; min-width: 0; }
+
+.agenda-btn {
+  flex-shrink: 0;
+  width: 2rem;
+  height: 2rem;
+  border: 1px solid #334155;
+  background: transparent;
+  border-radius: 0.4rem;
+  cursor: pointer;
+  font-size: 0.95rem;
+  opacity: 0.4;
+  transition: all 0.15s;
+  display: flex;
+  align-items: center;
+  justify-content: center;
+  padding: 0;
+}
+.agenda-btn:hover { opacity: 1; background: #334155; }
+.agenda-btn-set { opacity: 1; border-color: #6366f1; background: #1e1b4b; }
+
+.agenda-textarea {
+  width: 100%;
+  padding: 0.65rem 0.9rem;
+  background: #0f172a;
+  border: 1px solid #334155;
+  border-radius: 0.5rem;
+  color: #f1f5f9;
+  font-size: 0.9rem;
+  resize: vertical;
+  font-family: inherit;
+  line-height: 1.5;
+  box-sizing: border-box;
+}
+.agenda-textarea:focus { outline: none; border-color: #818cf8; }
+
+.dialog-hint {
+  font-size: 0.82rem;
+  color: #64748b;
+  margin: -0.5rem 0 0.25rem;
+}
+
 .strikes-list { display: flex; flex-direction: column; gap: 0.6rem; }
 
 .strikes-row {