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/components/admin/admin-shell.tsx

@@ -18,6 +18,7 @@ import Link from "next/link";
 import { usePathname } from "next/navigation";
 import {
   Bell,
+  Blocks,
   Database,
   FileText,
   Info,
@@ -39,6 +40,7 @@ import { cn } from "@/lib/utils";
 import { scrollBehaviorForUser } from "@/lib/motion";
 import { useAuth } from "@/hooks/use-auth";
 import { useTranslations } from "@/lib/i18n/context";
+import { SectionNavHeadingSpacer } from "@/components/settings/section-nav-heading-spacer";
 import { isAdminSectionSlug, type AdminSectionSlug } from "./section-slugs";
 
 interface AdminSection {
@@ -82,6 +84,13 @@ export const ADMIN_SECTIONS: readonly AdminSection[] = [
     titleKey: "admin.section.coach.title",
     icon: Sparkles,
   },
+  // v1.18.6 (W9) — server-wide module availability split out of Coach into
+  // its own entry, sitting next to it.
+  {
+    slug: "module-availability",
+    titleKey: "admin.section.module-availability.title",
+    icon: Blocks,
+  },
   {
     slug: "feedback",
     titleKey: "admin.section.feedback.title",
@@ -276,6 +285,9 @@ export function AdminShell({ active, children }: AdminShellProps) {
           className="hidden md:block"
         >
           <div className="sticky top-20">
+            {/* v1.18.6 (W9) — align the first nav item with the top of the
+                first card, matching the settings shell. */}
+            <SectionNavHeadingSpacer />
             <ul className="space-y-1">
               <li>
                 <Link

src/components/admin/section-slugs.ts

@@ -16,11 +16,15 @@ export const ADMIN_SECTION_SLUGS = [
   "integrations",
   // v1.18.1 — the former `ai-quality`, `assistant`, and `coach-feedback`
   // sections collapse into one "Coach" area. It holds the assistant
-  // surface toggles, the server-key + module-availability operator
-  // config, and both feedback-quality tables (Coach + Insights). Three
-  // navigation entries for one coherent coach-quality concern read as
-  // clutter; one card opens the full picture.
+  // surface toggles, the server-key operator config, and both
+  // feedback-quality tables (Coach + Insights). Three navigation entries
+  // for one coherent coach-quality concern read as clutter; one card opens
+  // the full picture.
   "coach",
+  // v1.18.6 (W9) — server-wide module availability is its own section now
+  // (was stacked under Coach). It gates every module, not just the coach,
+  // so it reads better next to Coach than buried inside it.
+  "module-availability",
   "feedback",
   "reminders",
   "users",