test(seam): make testseam the only seam-swap form and legislate it

- Add testseam.Protect for save-and-restore seams with no up-front stub
  value (e.g. os.Args mutated by the code under test).
- Migrate all 35 remaining manual prev/assign/t.Cleanup-restore trios to
  testseam.Swap/Protect across app, auth, cli, event, helpers, output,
  pipeline, and shortcut tests; restores can no longer be forgotten.
- check-schema-catalog.sh: fail closed when a manual seam restore
  reappears in any *_test.go (internal/testseam exempt).

Seam injection is now a mechanism, not a convention.

internal/shortcut/shortcut_test.go

@@ -23,6 +23,7 @@ import (
 	"github.com/DingTalk-Real-AI/dingtalk-workspace-cli/internal/corecmd/contract"
 	"github.com/DingTalk-Real-AI/dingtalk-workspace-cli/internal/corecmd/contractfinal"
 	apperrors "github.com/DingTalk-Real-AI/dingtalk-workspace-cli/internal/errors"
+	"github.com/DingTalk-Real-AI/dingtalk-workspace-cli/internal/testseam"
 	"github.com/DingTalk-Real-AI/dingtalk-workspace-cli/pkg/edition"
 	"github.com/spf13/cobra"
 )
@@ -474,9 +475,7 @@ func TestCrossPlatformCoverageBuildGroupsByService(t *testing.T) {
 }
 
 func TestBuiltInCommandsExcludeUserDefinedShortcuts(t *testing.T) {
-	previous := append([]Shortcut(nil), allShortcuts...)
-	t.Cleanup(func() { allShortcuts = previous })
-	allShortcuts = nil
+	testseam.Swap(t, &allShortcuts, []Shortcut(nil))
 	Register(
 		Shortcut{Service: "calendar", Command: "+builtin", Execute: noop},
 		Shortcut{Service: "calendar", Command: "+user", UserDefined: true, Execute: noop},