test: deploy-rs magic rollback verification

[stackptr]

Summary

• Adds a deliberately failing NixOS activation script on glyph to test deploy-rs magic rollback
• The activation script simply runs exit 1, which should cause deploy-rs to detect the failure and automatically roll back to the previous configuration
• This PR should be reverted after verifying rollback behavior

Expected behavior

1. CI builds successfully (activation scripts aren't run during build)
2. Deploy workflow runs and attempts to activate on glyph
3. Activation fails due to exit 1
4. deploy-rs detects the failure and rolls back to the previous profile
5. glyph remains on its previous working configuration

Test plan

• CI passes (build only, no activation)
• Deploy triggers and fails activation on glyph
• deploy-rs rolls back glyph automatically
• Revert this PR after confirming rollback works

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