feat(settings): standardize settings and admin section framing

Introduce a shared SettingsSectionFrame (the settings twin of the admin
renderer's SectionFrame) that emits the canonical visible heading +
subheading, and route all 19 settings sections through it. Every settings
page now shows a real h1 + subtitle in the reference Übersicht style
instead of an invisible sr-only title; the section bodies drop their own
headings and off-style intro paragraphs (the explanatory copy folds into
the frame subtitle).

- Route the admin About page through SectionFrame so it carries the same
  visible heading as every other admin section.
- Rename the AI settings section from KI-Auswertung to KI-Anbieter across
  six locales: the page configures the provider and key, not an analysis.
- Add a heading-block spacer to the settings and admin sidebars so the
  first menu item lines up with the top of the first card.
- Remove the always-on core-domains card from Module: a tracking area that
  can't be turned off doesn't need listing.
- Move the proactive-coach control out of Benachrichtigungen into Coach.
- Move admin module availability out of the Coach section into its own
  page: it gates every module, not just the coach.
- Give the Layout Insights editor a proper Insights heading.

Adds settings.sections.<slug>.subtitle and the new admin keys across all
six locales; removes the now-unused module core-domain strings.

src/app/admin/[section]/renderer.tsx

@@ -94,18 +94,32 @@ export function AdminSectionRenderer({
       // v1.18.1 — the former ai-quality, assistant, and coach-feedback
       // sections fold into one Coach area: surface toggles + operator
       // config first, then the two feedback-quality tables.
+      // v1.18.6 (W9) — server-wide module availability moved out to its own
+      // `module-availability` section: it gates EVERY module, not just the
+      // coach, so it no longer belongs stacked under Coach.
       return (
         <SectionFrame
           title={t("admin.section.coach.title")}
           subtitle={t("admin.section.coach.subtitle")}
         >
           <AssistantSection />
-          <ModuleAvailabilitySection />
           <AiServerKeySection />
           <CoachFeedbackSection />
           <AiQualitySection />
         </SectionFrame>
       );
+    case "module-availability":
+      // v1.18.6 (W9) — operator-side server-wide module on/off, its own
+      // admin section (was stacked under Coach). Reconciled name: the
+      // user-facing "Module" settings pick from what is available here.
+      return (
+        <SectionFrame
+          title={t("admin.section.module-availability.title")}
+          subtitle={t("admin.section.module-availability.subtitle")}
+        >
+          <ModuleAvailabilitySection />
+        </SectionFrame>
+      );
     case "feedback":
       return (
         <SectionFrame
@@ -191,12 +205,18 @@ export function AdminSectionRenderer({
         </SectionFrame>
       );
     case "about":
-      // v1.4.36 W4e — About section reused as-is from the settings
-      // surface. The component owns its own heading + cards layout
-      // so no SectionFrame wrapper.
-      // v1.18.6 — the About surface no longer carries the tour-replay card
-      // (consolidated onto Settings → Advanced), so there's nothing to hide.
-      return <AboutSection />;
+      // v1.4.36 W4e — About section reused as-is from the settings surface.
+      // v1.18.6 (W9) — route it through `SectionFrame` like every other admin
+      // section so it gets the same visible heading + subtitle (the one admin
+      // page that was bypassing the frame and showing no heading).
+      return (
+        <SectionFrame
+          title={t("admin.section.about.title")}
+          subtitle={t("admin.section.about.subtitle")}
+        >
+          <AboutSection />
+        </SectionFrame>
+      );
     default:
       slug satisfies never;
       return null;