DRY pass #2, batch 5, F17: the web's smaller pairs (#5372)

- desktop/bridge.ts listen<T>(): the no-op-off-desktop event listener
  that onSynced, onCaptured and onReminderDue each wrote.
- size.ts roughSize(): one decimal below 10, none above, for the client
  download sizes (MB) and the storage line (GB).
- BaseModal's title prop draws the heading row and close button that
  LabelsModal and ShareDialog each built.
- SyncView: switchChannel and switchSource share recheck(); the four
  update-card radios render from two option lists.

Kept: the board's and the shell's is-typing guards (they ignore different
elements), the drawer's nav beside the palette's commands (one is a laid-
out list with tags between its entries, the other a command list), the
status pills (each colours differently), and plurals (the copy is the
operator's call, raised in #5371).

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

frontend/src/components/LabelsModal.vue

@@ -58,11 +58,7 @@ async function doMerge(sourceId: string, targetId: string) {
 </script>
 
 <template>
-  <BaseModal panel-class="w-full max-w-sm shadow-xl" @close="emit('close')">
-    <div class="flex items-center justify-between border-b border-neutral-100 px-4 py-3 dark:border-neutral-800">
-        <h2 class="text-sm font-semibold">Manage tags</h2>
-        <button type="button" class="icon-btn" aria-label="Close" @click="emit('close')"><Icon name="close" /></button>
-      </div>
+  <BaseModal panel-class="w-full max-w-sm shadow-xl" title="Manage tags" @close="emit('close')">
       <div class="flex flex-col gap-2 p-4">
         <form class="flex items-center gap-2" @submit.prevent="add">
           <Icon name="plus" />