test: update yacht-prereq error message assertion to match F21 copy

The integration test was pinned to the legacy "yachtId is required before
leaving stage=enquiry" developer-language string. F21 reworded it to
"A yacht must be linked before leaving the Enquiry stage." for the toast
surface — bring the test regex along.

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

tests/integration/interests-yacht.test.ts

@@ -157,7 +157,7 @@ describe('interests.service — yacht ownership validation', () => {
         { pipelineStage: 'qualified' },
         makeAuditMeta({ portId: port.id }),
       ),
-    ).rejects.toThrow(/yachtId is required before leaving stage=enquiry/);
+    ).rejects.toThrow(/yacht must be linked before leaving the Enquiry stage/i);
   });
 
   it('changeInterestStage succeeds when yachtId is set', async () => {