refactor(v1.5): apply simplify-review safe-to-apply suggestions

Drops dead `id` props and `scroll-mt-28` classes from admin section
components (load-bearing in v1.4 monolithic admin, dead since the v1.5
phase-4b dynamic-route split). Also removes the unused
`LEGACY_ANCHOR_TO_SLUG` map, the `admin-shell` re-export shim, the
`BERLIN_TZ` and duplicate `MS_PER_DAY` constants, the verbose
`AdminSectionPage` docstring, the `useEffect` paraphrase comment in
`ai-section`, and rewrites the `_exhaustive: never` exhaustiveness
guard to the modern `slug satisfies never` form. `UserManagementSection`
now reads `currentUserId` via `useAuth()` instead of accepting it as a
prop.

Findings 1, 2, 3, 4, 6, 7, 8, 11, 15, 16, 17 from
.planning/phase-6-simplify-findings.md.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

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

@@ -7,19 +7,8 @@ import {
   isAdminSectionSlug,
 } from "@/components/admin/section-slugs";
 
-/**
- * Dynamic admin section route — mirrors the v1.4 settings split. Each of
- * the `ADMIN_SECTION_SLUGS` is pre-rendered at build via
- * `generateStaticParams()` so the URLs are statically known to Next.js,
- * while `dynamicParams = false` tells the router to 404 (rather than
- * attempting on-demand rendering) for any slug not in the list.
- *
- * The actual section components are mounted by the client-only
- * `<AdminSectionRenderer>` because most of them use TanStack Query and
- * the auth hook (server-rendered they'd just paint a loader). The shell,
- * however, is server-rendered so the sidebar paints with no JS hydration
- * lag.
- */
+// Section bodies need TanStack Query / useAuth, so they're rendered by the
+// client-only `<AdminSectionRenderer>`. The shell stays server-rendered.
 
 export const dynamicParams = false;
 
@@ -28,16 +17,12 @@ export function generateStaticParams() {
 }
 
 interface PageProps {
-  // Next.js 16 made route `params` an async Promise. We `await` it before use.
   params: Promise<{ section: string }>;
 }
 
 export default async function AdminSectionPage({ params }: PageProps) {
   const { section } = await params;
 
-  // Defence-in-depth — `dynamicParams = false` already 404s unknown slugs at
-  // routing time, but we re-check here so a hand-rolled override of the
-  // route config can never silently fall through to a typo'd slug.
   if (!isAdminSectionSlug(section)) {
     notFound();
   }

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

@@ -106,7 +106,7 @@ export function AdminSectionRenderer({
           title={t("admin.section.users.title")}
           subtitle={t("admin.section.users.subtitle")}
         >
-          <UserManagementSection currentUserId={user.id} />
+          <UserManagementSection />
         </SectionFrame>
       );
     case "api-tokens":
@@ -145,12 +145,9 @@ export function AdminSectionRenderer({
           <DangerZoneSection />
         </SectionFrame>
       );
-    default: {
-      // exhaustiveness guard — TS will flag a missing case here
-      const _exhaustive: never = slug;
-      void _exhaustive;
+    default:
+      slug satisfies never;
       return null;
-    }
   }
 }