fix(frontend): refresh task list after sync

[prodriguezxyz]

Summary

syncTasks in the Vuex store posts to /api/sync but does not refetch the task list afterwards, so the in-memory state stays stale until the user reloads the page. Any change pulled in by task sync (added, modified, or deleted tasks from another device) is invisible in the UI until F5.

This PR aligns syncTasks with the existing pattern used by deleteTasks and updateTasks — dispatch fetchTasks once the write completes.

Change

-async syncTasks(_context) {
+async syncTasks(context) {
     await this.\$axios.\$post('/api/sync');
+    await context.dispatch('fetchTasks');
 }

Test plan

• Trigger a sync from the sync icon in the toolbar — tasks refresh without a manual reload.
• Add/modify/delete a task on another device, run sync from the UI — the change appears immediately.
• Behaviour of deleteTasks / updateTasks unchanged (they already did this).

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