Add Day Started event to activity log with template name

- On session start, insert a session_start TimerEvent so the action
  appears in the activity log timeline
- Load DailySession.template via selectinload in the timeline query
  so the template name is available without extra round-trips
- _to_timeline_out maps the template name into block_label for
  session_start events, displaying as "Day started — Template Name"
- Add session_start to EVENT_META on the frontend (🏫 icon)
- Hide the Edit button for session_start entries since changing their
  event type to a block-level action doesn't make sense

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

frontend/src/views/LogView.vue

@@ -101,7 +101,7 @@
                   </div>
                 </div>
                 <div class="row-actions">
-                  <button class="btn-sm" @click="startEdit(entry)">Edit</button>
+                  <button class="btn-sm" v-if="entry.event_type !== 'session_start'" @click="startEdit(entry)">Edit</button>
                   <button class="btn-sm btn-danger" @click="deleteEntry(entry)">✕</button>
                 </div>
               </div>
@@ -183,11 +183,12 @@ function fmtTime(isoStr) {
 }
 
 const EVENT_META = {
-  start:    { icon: '▶', label: 'Started' },
-  pause:    { icon: '⏸', label: 'Paused' },
-  resume:   { icon: '↺', label: 'Resumed' },
-  complete: { icon: '✓', label: 'Completed' },
-  skip:     { icon: '⟶', label: 'Skipped' },
+  session_start: { icon: '🏫', label: 'Day started' },
+  start:         { icon: '▶', label: 'Started' },
+  pause:         { icon: '⏸', label: 'Paused' },
+  resume:        { icon: '↺', label: 'Resumed' },
+  complete:      { icon: '✓', label: 'Completed' },
+  skip:          { icon: '⟶', label: 'Skipped' },
 }
 
 function eventIcon(entry) {