Add Reset button and move End Day to right side of actions bar

Reset clears the current block's elapsed time to zero and immediately
starts the timer. A shared compute_block_elapsed() utility (utils/timer.py)
handles the elapsed calculation in both the sessions and dashboard routers,
and correctly treats "reset" events as zero-elapsed restart markers so
page reloads after a reset show accurate times.

Layout: Start/Pause/Resume/Reset are grouped on the left; End Day sits
on the right via justify-content: space-between.

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

frontend/src/stores/schedule.js

@@ -101,6 +101,13 @@ export const useScheduleStore = defineStore('schedule', () => {
       blockStartedAt.value = Date.now()
       isPaused.value = false
     }
+    // Reset — clear elapsed to 0 and start counting immediately
+    if (event.event === 'reset') {
+      if (event.block_id) blockElapsedCache.value[event.block_id] = 0
+      blockElapsedOffset.value = 0
+      blockStartedAt.value = Date.now()
+      isPaused.value = false
+    }
     // Select — switch current block but keep timer stopped (manual start required)
     if (event.event === 'select') {
       // Sync the previous block's cache
@@ -204,6 +211,17 @@ export const useScheduleStore = defineStore('schedule', () => {
     sendTimerAction(sessionId, 'start', session.value.current_block_id)
   }
 
+  // Reset the current block's timer to 0 and start counting immediately.
+  function resetCurrentBlock(sessionId) {
+    if (!session.value?.current_block_id) return
+    const blockId = session.value.current_block_id
+    blockElapsedCache.value[blockId] = 0
+    blockElapsedOffset.value = 0
+    isPaused.value = false
+    blockStartedAt.value = Date.now()
+    sendTimerAction(sessionId, 'reset', blockId)
+  }
+
   return {
     session,
     blocks,
@@ -226,5 +244,6 @@ export const useScheduleStore = defineStore('schedule', () => {
     switchBlock,
     selectBlock,
     startCurrentBlock,
+    resetCurrentBlock,
   }
 })