Inhibit command on script and generalize single-tab bar hiding

[sbertix]

Summary

• Replace tmux-specific tab bar hiding with a general "Hide Tab Bar for Single Tab" setting (hideSingleTabBar), with legacy migration for the old hideTmuxTabBar key.
• Pass an explicit command and environmentVariables through GhosttySurfaceView so blocking scripts can launch with a controlled shell and script environment.
• Add a copy-to-clipboard button for script variable keys in repository settings.

Test plan

• Verify the "Hide Tab Bar for Single Tab" toggle works in Appearance settings.
• Confirm existing hideTmuxTabBar persisted settings migrate correctly to hideSingleTabBar.
• Test that blocking scripts launch with the correct command and environment variables.
• Test the copy button for variable keys in repository settings.

Closes #217, #219