feat(tenancies-p6): module-gate entity tabs (berth / client / yacht)

- PortProvider exposes tenanciesModuleByPort + a useTenanciesModuleEnabled()
  hook that returns the flag for the currently-active port. Synchronous
  read off context (server-resolved in the dashboard layout), so no
  fetch latency / hydration flicker when the rep flips ports.
- buildBerthTabs / getClientTabs / getYachtTabs gain a
  tenanciesModuleEnabled option. When false, the Tenancies tab is
  filtered out entirely. When true, it slots into the entity-specific
  position (after Interests on berth + yacht; after Companies on client).
- BerthDetail / ClientDetail / YachtDetail pass the hook value through.
  Hook call ordered above the early-return so React's rules-of-hooks
  stays satisfied. Existing read-only tab content (Active tenancy card
  + History + the berth-side BerthReserveDialog "Create tenancy" CTA
  from P2) stays untouched — it just becomes visible when the module
  is on.

Deferred (separate ship): generic TenancyCreateDialog that pre-fills
clientId / yachtId from the parent entity context, so client / yacht
tabs can mint a tenancy without bouncing through the berth detail page.
Today client/yacht Tenancies tabs are read-only (the create entry-point
is the berth tab); the generic dialog will land alongside the Edit /
Renew / Transfer / End dialogs (design § P6 sub-tasks).

Verified: tsc clean, 1493/1493 vitest.

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

src/providers/port-provider.tsx

@@ -12,6 +12,10 @@ interface PortContextValue {
   currentPort: Port | null;
   currentPortId: string | null;
   currentPortSlug: string | null;
+  /** Per-port feature-flag map — currently just the Tenancies module.
+   *  Resolved server-side in the dashboard layout. Consumers read via
+   *  `useTenanciesModuleEnabled()`. */
+  tenanciesModuleByPort: Record<string, boolean>;
 }
 
 const PortContext = createContext<PortContextValue>({
@@ -19,15 +23,22 @@ const PortContext = createContext<PortContextValue>({
   currentPort: null,
   currentPortId: null,
   currentPortSlug: null,
+  tenanciesModuleByPort: {},
 });
 
 interface PortProviderProps {
   children: ReactNode;
   ports: Port[];
   defaultPortId: string | null;
+  tenanciesModuleByPort?: Record<string, boolean>;
 }
 
-export function PortProvider({ children, ports, defaultPortId }: PortProviderProps) {
+export function PortProvider({
+  children,
+  ports,
+  defaultPortId,
+  tenanciesModuleByPort = {},
+}: PortProviderProps) {
   const params = useParams();
   const portSlugFromUrl = params?.portSlug as string | undefined;
 
@@ -75,6 +86,7 @@ export function PortProvider({ children, ports, defaultPortId }: PortProviderPro
         currentPort: currentPort ?? null,
         currentPortId: currentPort?.id ?? null,
         currentPortSlug: currentPort?.slug ?? null,
+        tenanciesModuleByPort,
       }}
     >
       {children}
@@ -85,3 +97,12 @@ export function PortProvider({ children, ports, defaultPortId }: PortProviderPro
 export function usePortContext(): PortContextValue {
   return useContext(PortContext);
 }
+
+/** Read the tenancies-module-enabled flag for the currently-active port.
+ *  Server-side resolved in the dashboard layout, so this is a synchronous
+ *  read with no fetch latency or hydration flicker. */
+export function useTenanciesModuleEnabled(): boolean {
+  const { currentPortId, tenanciesModuleByPort } = useContext(PortContext);
+  if (!currentPortId) return false;
+  return tenanciesModuleByPort[currentPortId] ?? false;
+}