fix(build): extract route.ts handlers to handlers.ts (CLAUDE.md convention)

8 API route files were exporting handler functions directly from route.ts,
which Next.js 15 rejects with "$NAME is not a valid Route export field".
Per CLAUDE.md convention, service-tested handler functions live in sibling
handlers.ts files and route.ts only re-exports the GET/POST/etc. wrapped
in withAuth(withPermission(...)).

Discovered during the mobile-foundation Task 24 build validation; the route
files predate this branch but the build was never re-run on data-model.

Files:
- berth-reservations/[id], companies/autocomplete, companies/[id]/members
  + nested mid/set-primary, yachts/autocomplete, yachts/[id]/transfer,
  yachts/[id]/ownership-history
- Integration tests updated to import from handlers.ts (companies,
  memberships, reservations, yachts-detail)

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

src/app/api/v1/yachts/[id]/ownership-history/route.ts

@@ -1,16 +1,5 @@
-import { NextResponse } from 'next/server';
+import { withAuth, withPermission } from '@/lib/api/helpers';
 
-import { withAuth, withPermission, type RouteHandler } from '@/lib/api/helpers';
-import { errorResponse } from '@/lib/errors';
-import { listOwnershipHistory } from '@/lib/services/yachts.service';
-
-export const historyHandler: RouteHandler = async (req, ctx, params) => {
-  try {
-    const history = await listOwnershipHistory(params.id!, ctx.portId);
-    return NextResponse.json({ data: history });
-  } catch (error) {
-    return errorResponse(error);
-  }
-};
+import { historyHandler } from './handlers';
 
 export const GET = withAuth(withPermission('yachts', 'view', historyHandler));