fix: add missing _count to getRepositoryById test mock

The mock for repositories.findUnique was missing the _count field
that Prisma returns when using include: { _count: { select: ... } }.
This caused repo._count.repository_members to throw, which the catch
block swallowed and returned null, making all 3 "successful retrieval"
tests fail with "Cannot read properties of null (reading 'is_active')".

Add _count: { repository_members: 2 } to match the actual Prisma
return shape. All 39 tests now pass.

js/cf-webapp/src/app/(dashboard)/repositories/[repositoryId]/__tests__/action.test.ts

@@ -28,6 +28,8 @@ const mockRepo = {
   optimizations_limit: 100,
   optimizations_used: 50,
   repository_members: [{ id: "rm-1" }, { id: "rm-2" }],
+  // Matches the Prisma return shape for include: { _count: { select: { repository_members: true } } }
+  _count: { repository_members: 2 },
 }
 
 const mockPayload = { userId: "user-1", username: "testuser" }