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/components/layout/app-shell.tsx

@@ -24,6 +24,9 @@ interface AppShellProps {
   /** Per-port logo URLs resolved server-side. Sidebar picks the entry
    *  matching the currently-active port from the UI store. */
   portLogoUrls: Record<string, string | null>;
+  /** Per-port `tenancies_module_enabled` resolution. Gates the Tenancies
+   *  sidebar entry SSR-side so the nav doesn't flicker in/out. */
+  tenanciesModuleByPort: Record<string, boolean>;
   /**
    * Server-rendered form-factor hint (from the request User-Agent). The
    * shell mounts the matching tree on first render so we never paint the
@@ -86,6 +89,7 @@ export function AppShell({
   user,
   ports,
   portLogoUrls,
+  tenanciesModuleByPort,
   initialFormFactor,
   children,
 }: AppShellProps) {
@@ -137,6 +141,7 @@ export function AppShell({
     user,
     ports,
     portLogoUrls,
+    tenanciesModuleByPort,
   };
 
   // Chrome subtree per tier.

src/components/layout/sidebar.tsx

@@ -9,6 +9,7 @@ import {
   Users,
   Bookmark,
   Anchor,
+  KeyRound,
   Ship,
   Building2,
   Receipt,
@@ -51,6 +52,9 @@ interface SidebarProps {
    *  The sidebar header swaps to the current port's logo via the UI
    *  store's `currentPortId`. Null entries render the wordmark fallback. */
   portLogoUrls?: Record<string, string | null>;
+  /** Per-port `tenancies_module_enabled` resolution. Gates the Tenancies
+   *  sidebar entry. Resolved server-side in the dashboard layout. */
+  tenanciesModuleByPort?: Record<string, boolean>;
 }
 
 interface NavItem {
@@ -72,6 +76,12 @@ interface NavSection {
   umamiRequired?: boolean;
 }
 
+interface NavItemGated extends NavItem {
+  /** When true, only render this item if the tenancies module is enabled
+   *  for the current port. Resolved against `tenanciesModuleByPort`. */
+  requiresTenanciesModule?: boolean;
+}
+
 function buildNavSections(portSlug: string | undefined): NavSection[] {
   const base = portSlug ? `/${portSlug}` : '';
 
@@ -86,6 +96,12 @@ function buildNavSections(portSlug: string | undefined): NavSection[] {
         { href: `${base}/companies`, label: 'Companies', icon: Building2 },
         { href: `${base}/interests`, label: 'Interests', icon: Bookmark },
         { href: `${base}/berths`, label: 'Berths', icon: Anchor },
+        {
+          href: `${base}/tenancies`,
+          label: 'Tenancies',
+          icon: KeyRound,
+          requiresTenanciesModule: true,
+        } as NavItemGated,
       ],
     },
     {
@@ -235,6 +251,7 @@ function SidebarContent({
   hasAdminAccess,
   hasMarinaAccess,
   hasResidentialAccess,
+  tenanciesModuleEnabled,
   user,
   ports,
   currentPort,
@@ -248,6 +265,7 @@ function SidebarContent({
   hasAdminAccess: boolean;
   hasMarinaAccess: boolean;
   hasResidentialAccess: boolean;
+  tenanciesModuleEnabled: boolean;
   user?: SidebarProps['user'];
   ports?: Port[];
   currentPort: Port | null;
@@ -366,15 +384,22 @@ function SidebarContent({
                   )}
                   {(!section.adminRequired || adminExpanded || collapsed) && (
                     <ul className="space-y-0.5">
-                      {section.items.map((item) => (
-                        <li key={item.href}>
-                          <NavItemLink
-                            item={item}
-                            collapsed={collapsed}
-                            active={isActive(item.href, item.exact)}
-                          />
-                        </li>
-                      ))}
+                      {section.items
+                        .filter((item) => {
+                          const gated = item as NavItemGated;
+                          if (gated.requiresTenanciesModule && !tenanciesModuleEnabled)
+                            return false;
+                          return true;
+                        })
+                        .map((item) => (
+                          <li key={item.href}>
+                            <NavItemLink
+                              item={item}
+                              collapsed={collapsed}
+                              active={isActive(item.href, item.exact)}
+                            />
+                          </li>
+                        ))}
                     </ul>
                   )}
                   <Separator className="mt-3 bg-slate-200" aria-hidden />
@@ -456,6 +481,7 @@ export function Sidebar({
   user,
   ports,
   portLogoUrls,
+  tenanciesModuleByPort,
 }: SidebarProps) {
   // Sidebar collapse removed - design preference is the always-expanded
   // form. Forcibly false; the store flag stays for backwards-compat with
@@ -465,6 +491,9 @@ export function Sidebar({
   const currentPortId = useUIStore((s) => s.currentPortId);
   const currentPort = ports?.find((p) => p.id === currentPortId) ?? ports?.[0] ?? null;
   const currentLogoUrl = currentPortId ? (portLogoUrls?.[currentPortId] ?? null) : null;
+  const tenanciesModuleEnabled = currentPortId
+    ? (tenanciesModuleByPort?.[currentPortId] ?? false)
+    : false;
 
   // Super admins see every section regardless of role rows.
   const hasAdminAccess =
@@ -496,6 +525,7 @@ export function Sidebar({
         hasAdminAccess={hasAdminAccess}
         hasMarinaAccess={hasMarinaAccess}
         hasResidentialAccess={hasResidentialAccess}
+        tenanciesModuleEnabled={tenanciesModuleEnabled}
         user={user}
         ports={ports}
         currentPort={currentPort}