style(ia): wave 4 — one section-header language across every admin surface

The Subscriptions Settings tab's bare text-h6 headers adopt the same
uppercase accent section-title + hint convention Maintenance/Cleanup use, with
a one-line hint per section (extension / credentials / downloader / external
file-hosts / schedule defaults). Every settings-ish surface now reads
identically.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01CDgx8bQS5YrGRK76v8HUnM

frontend/src/components/subscriptions/SettingsTab.vue

@@ -4,7 +4,8 @@
          from Settings → Overview) + the API key bar it authenticates with.
          The extension feeds THIS view — cookies + one-click sources — so its
          setup lives with the rest of the ingestion config. -->
-    <h3 class="text-h6 mb-3">Browser extension</h3>
+    <h3 class="fc-section__title">Browser extension</h3>
+    <p class="fc-section__hint">Install, session cookies and the API key it authenticates with.</p>
     <BrowserExtensionCard class="mb-3" />
     <ExtensionKeyBar class="mb-4" />
 
@@ -12,7 +13,8 @@
       {{ String(credentialsStore.error) }}
     </v-alert>
 
-    <h3 class="text-h6 mb-3 mt-6">Platform credentials</h3>
+    <h3 class="fc-section__title mt-6">Platform credentials</h3>
+    <p class="fc-section__hint">Per-platform cookies/tokens the downloader uses.</p>
     <v-row>
       <v-col
         v-for="p in platformsStore.list"
@@ -29,7 +31,8 @@
       </v-col>
     </v-row>
 
-    <h3 class="text-h6 mb-3 mt-6">Downloader</h3>
+    <h3 class="fc-section__title mt-6">Downloader</h3>
+    <p class="fc-section__hint">Rate limits and gallery-dl behavior for source checks.</p>
     <v-card variant="outlined">
       <v-card-text v-if="importStore.settings">
         <v-row>
@@ -58,7 +61,8 @@
       </v-card-text>
     </v-card>
 
-    <h3 class="text-h6 mb-3 mt-6">External file-host downloads</h3>
+    <h3 class="fc-section__title mt-6">External file-host downloads</h3>
+    <p class="fc-section__hint">Post-linked mega/gdrive/file-host fetches.</p>
     <v-card variant="outlined">
       <v-card-text v-if="importStore.settings">
         <div class="fc-help mb-2">
@@ -104,7 +108,8 @@
       </v-card-text>
     </v-card>
 
-    <h3 class="text-h6 mb-3 mt-6">Schedule defaults</h3>
+    <h3 class="fc-section__title mt-6">Schedule defaults</h3>
+    <p class="fc-section__hint">Check cadence and failure-badge thresholds for new sources.</p>
     <v-card variant="outlined">
       <v-card-text v-if="importStore.settings">
         <v-row>
@@ -247,6 +252,21 @@ async function saveDownloader() {
 </script>
 
 <style scoped>
+/* Same section-header language as Settings -> Maintenance/Cleanup (2026-07-02
+   theme unification) so every admin surface reads identically. */
+.fc-section__title {
+  font-size: 0.78rem;
+  font-weight: 700;
+  letter-spacing: 0.06em;
+  text-transform: uppercase;
+  color: rgb(var(--v-theme-accent));
+  margin-bottom: 2px;
+}
+.fc-section__hint {
+  font-size: 0.8rem;
+  color: rgb(var(--v-theme-on-surface-variant));
+  margin-bottom: 12px;
+}
 .fc-help {
   font-size: 12px;
   color: rgb(var(--v-theme-on-surface-variant));