test(recommendation): fix mislabeled compile-time assert in home tests

Replaces var _ = func() pgtype.UUID { ... } with var _ map[pgtype.UUID]struct{}
which actually verifies map-key comparability, matching the comment.

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

internal/recommendation/home_integration_test.go

@@ -39,7 +39,7 @@ func TestHomeData_NewUser_AllSectionsEmpty(t *testing.T) {
 // Compile-time assert that pgtype.UUID is a valid map key — used by the
 // service when de-duping rediscover fallback rows. If this changes, the
 // service needs to switch to keying by string.
-var _ = func() pgtype.UUID { return pgtype.UUID{} }
+var _ map[pgtype.UUID]struct{}
 
 func TestHomeData_RecentlyAdded_OrderedByCreatedAt(t *testing.T) {
 	pool := newPool(t)