DRY pass #2, batch 5, F14: the web's repeated class lists become component classes (#5372)

style.css gains the classes the views spelled out in full: .section-label
(17 sites), .hint (20), .form-error (13), .alert-error (5), .row-card (5),
.list-empty (5), .field (5), .page-shell (3), and the small row action
.btn-sm (4) / .btn-sm-danger (3). Only exact runs moved, so nothing renders
differently; spacing a site adds beyond a run stays a utility beside it.

Kept: the Reminders and Timeline small buttons. They carry no text colour
and inherit it, so putting them on .btn-sm would recolour them.

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

frontend/src/components/ActivityList.vue

@@ -93,11 +93,11 @@ onMounted(() => {
 
 <template>
   <section class="flex flex-col gap-5">
-    <h2 class="text-xs font-semibold uppercase tracking-wide text-neutral-400">Activity</h2>
+    <h2 class="section-label">Activity</h2>
 
-    <p v-if="error" class="text-sm text-red-600 dark:text-red-400">{{ error }}</p>
+    <p v-if="error" class="form-error">{{ error }}</p>
 
-    <div v-if="loading" class="py-6 text-center text-sm text-neutral-400">Loading…</div>
+    <div v-if="loading" class="list-empty">Loading…</div>
     <p v-else-if="!events.length" class="text-sm text-neutral-400">Nothing yet.</p>
     <ul v-else class="flex flex-col gap-2">
       <li
@@ -118,7 +118,7 @@ onMounted(() => {
     <button
       v-if="more"
       type="button"
-      class="self-start rounded-md border border-neutral-300 px-2.5 py-1 text-xs text-neutral-700 hover:bg-neutral-100 focus:outline-none focus-visible:ring-2 focus-visible:ring-brand disabled:opacity-50 dark:border-neutral-700 dark:text-neutral-200 dark:hover:bg-neutral-800"
+      class="self-start btn-sm"
       :disabled="loadingMore"
       @click="loadMore"
     >