feat(tenancies-p5): sidebar entry + 404 top-level page + API module gate

- Dashboard layout resolves tenanciesModuleByPort server-side (one
  isTenanciesModuleEnabled call per port the user has access to) and
  passes the map through AppShell → Sidebar. Atomic SSR — no
  flicker of the nav entry in/out after hydration.
- Sidebar gains NavItemGated.requiresTenanciesModule. The Tenancies
  entry (KeyRound icon, immediately below Berths) only renders when
  the currently-active port has the flag flipped on. Per-port live
  switch fires when the rep toggles ports without reload.
- /[portSlug]/tenancies + /[portSlug]/tenancies/[id] both call
  isTenanciesModuleEnabled and notFound() when disabled — guards
  against direct URL access even when the sidebar is hidden.
- API routes (/api/v1/tenancies, /[id], /berths/[id]/tenancies)
  prepended with assertTenanciesModuleEnabled — matches design §
  "All routes ... return 404 when off". NotFoundError maps to 404.
- Existing tenancy API tests get a makePortWithTenancies() helper
  (calls enableTenanciesModule after makePort) so the gate is
  satisfied. Affects 2 test files (16 tests retargeted).

Verified: tsc clean, 1493/1493 vitest.

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

src/app/(dashboard)/[portSlug]/tenancies/[id]/page.tsx

@@ -1,4 +1,10 @@
+import { notFound } from 'next/navigation';
+import { eq } from 'drizzle-orm';
+
 import { TenancyDetail } from '@/components/tenancies/tenancy-detail';
+import { db } from '@/lib/db';
+import { ports as portsTable } from '@/lib/db/schema/ports';
+import { isTenanciesModuleEnabled } from '@/lib/services/tenancies-module.service';
 
 interface PageProps {
   params: Promise<{ portSlug: string; id: string }>;
@@ -6,5 +12,12 @@ interface PageProps {
 
 export default async function TenancyDetailPage({ params }: PageProps) {
   const { portSlug, id } = await params;
+  const port = await db.query.ports.findFirst({
+    where: eq(portsTable.slug, portSlug),
+    columns: { id: true },
+  });
+  if (!port) notFound();
+  if (!(await isTenanciesModuleEnabled(port.id))) notFound();
+
   return <TenancyDetail tenancyId={id} portSlug={portSlug} />;
 }

src/app/(dashboard)/[portSlug]/tenancies/page.tsx

@@ -1,5 +1,26 @@
-import { TenanciesListPage } from '@/components/tenancies/tenancies-list-page';
+import { notFound } from 'next/navigation';
+
+import { TenanciesListPage } from '@/components/tenancies/tenancies-list-page';
+import { db } from '@/lib/db';
+import { ports as portsTable } from '@/lib/db/schema/ports';
+import { eq } from 'drizzle-orm';
+import { isTenanciesModuleEnabled } from '@/lib/services/tenancies-module.service';
+
+interface PageProps {
+  params: Promise<{ portSlug: string }>;
+}
+
+export default async function BerthTenanciesPage({ params }: PageProps) {
+  const { portSlug } = await params;
+  // Per docs/tenancies-design.md §"When disabled": top-level page returns
+  // 404 when the module is off. The sidebar entry is already hidden via
+  // tenanciesModuleByPort, so this 404 guards against direct URL access.
+  const port = await db.query.ports.findFirst({
+    where: eq(portsTable.slug, portSlug),
+    columns: { id: true },
+  });
+  if (!port) notFound();
+  if (!(await isTenanciesModuleEnabled(port.id))) notFound();
 
-export default function BerthTenanciesPage() {
   return <TenanciesListPage />;
 }