feat(api): GET/POST /api/v1/yachts

Add yacht list + create routes, export RouteHandler type and inner
handlers so tests can invoke them directly with a mock AuthContext.
New tests/helpers/route-tester.ts provides makeMockCtx/makeMockRequest
reusable by subsequent Task 3.x routes.

tests/helpers/route-tester.ts

@@ -0,0 +1,42 @@
+/**
+ * Helper to invoke route inner-handlers directly, bypassing withAuth.
+ * Route files must export the inner handler (in addition to the withAuth-wrapped HTTP method).
+ */
+import { NextRequest } from 'next/server';
+import type { AuthContext } from '@/lib/api/helpers';
+import type { RolePermissions } from '@/lib/db/schema/users';
+
+export interface MockCtxOptions {
+  portId: string;
+  isSuperAdmin?: boolean;
+  permissions?: RolePermissions | null;
+  userId?: string;
+}
+
+export function makeMockCtx(opts: MockCtxOptions): AuthContext {
+  return {
+    userId: opts.userId ?? 'test-user',
+    portId: opts.portId,
+    portSlug: 'test-port',
+    isSuperAdmin: opts.isSuperAdmin ?? false,
+    permissions: opts.permissions ?? null,
+    user: { email: 'test@example.com', name: 'Test User' },
+    ipAddress: '127.0.0.1',
+    userAgent: 'vitest/1.0',
+  };
+}
+
+export function makeMockRequest(
+  method: string,
+  url: string,
+  opts: { body?: unknown; headers?: Record<string, string> } = {},
+): NextRequest {
+  const init: { method: string; headers: Record<string, string>; body?: string } = {
+    method,
+    headers: { 'content-type': 'application/json', ...(opts.headers ?? {}) },
+  };
+  if (opts.body !== undefined) {
+    init.body = JSON.stringify(opts.body);
+  }
+  return new NextRequest(url, init);
+}