feat(rig): support parking multiple rigs in single call

- gt rig park now accepts variadic args (fixes #375)
- gt rig unpark updated for consistency
- Errors collected and reported at end

Also fixes test self-interruption bug where sling tests sent real
tmux nudges containing "Work slung: gt-wisp-xyz", causing agents
running tests to interrupt themselves. Added GT_TEST_NO_NUDGE env
var to skip nudge during tests.

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

internal/cmd/sling_test.go

@@ -292,6 +292,9 @@ exit 0
 	slingVars = nil
 	slingOnTarget = "gt-abc123"
 
+	// Prevent real tmux nudge from firing during tests (causes agent self-interruption)
+	t.Setenv("GT_TEST_NO_NUDGE", "1")
+
 	if err := runSling(nil, []string{"mol-review"}); err != nil {
 		t.Fatalf("runSling: %v", err)
 	}
@@ -452,6 +455,9 @@ exit 0
 	slingVars = nil
 	slingOnTarget = "gt-abc123"
 
+	// Prevent real tmux nudge from firing during tests (causes agent self-interruption)
+	t.Setenv("GT_TEST_NO_NUDGE", "1")
+
 	if err := runSling(nil, []string{"mol-review"}); err != nil {
 		t.Fatalf("runSling: %v", err)
 	}