test(tenant): cover desktop task platform id dedup and target count

Assert uniqueMonitorDesktopTaskPlatformIDs trims and collapses duplicate
account specs, and tighten the healthier-candidate case with a target
length check. Apply gofmt alignment fixes.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

server/internal/tenant/app/monitoring_phase2_desktop_tasks_test.go

@@ -121,12 +121,24 @@ func TestSelectMonitorDesktopTaskTargetsPrefersHealthierOnlineCandidate(t *testi
 		0,
 	)
 
+	require.Len(t, targets, 1)
 	assert.Equal(t, monitorDesktopTaskTarget{
 		AccountID: liveAccountID,
 		ClientID:  liveClientID,
 	}, targets["qwen"])
 }
 
+func TestUniqueMonitorDesktopTaskPlatformIDsCollapsesDuplicateAccountSpecs(t *testing.T) {
+	platformIDs := uniqueMonitorDesktopTaskPlatformIDs([]monitorDesktopTaskSpec{
+		{PlatformID: "doubao"},
+		{PlatformID: " doubao "},
+		{PlatformID: "qwen"},
+		{PlatformID: ""},
+	})
+
+	assert.Equal(t, []string{"doubao", "qwen"}, platformIDs)
+}
+
 func TestSelectMonitorDesktopTaskTargetsPrefersEarlierOnlineClientForSameAccount(t *testing.T) {
 	accountID := mustParseDailyMonitoringUUID(t, "00000000-0000-0000-0000-000000000501")
 	earlierClientID := mustParseDailyMonitoringUUID(t, "00000000-0000-0000-0000-000000000601")