Fix LaunchOnlyOnce contradiction in key rotation LaunchAgent

[Copilot]

Description

The com.shawnschwartz.cassh.rotate.plist LaunchAgent had LaunchOnlyOnce=false with a comment stating "Don't run if already running" — contradictory behavior. Setting LaunchOnlyOnce=false allows launchd to spawn concurrent instances when StartInterval fires.

Changed:

• Removed LaunchOnlyOnce key (defaults to preventing concurrent runs for StartInterval jobs)
• Removed misleading comment

The default behavior now correctly prevents overlapping key rotation executions without requiring lock file implementation.

Type of Change

• Bug fix (non-breaking change that fixes an issue)
• New feature (non-breaking change that adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• Documentation update
• Refactoring (no functional changes)

Related Issues

Part of #7 feedback

How Has This Been Tested?

• Manual testing

Test environment:

• OS: macOS
• Go version: N/A (plist configuration change only)

Checklist

• My code follows the project's style guidelines
• I have performed a self-review of my code
• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation
• My changes generate no new warnings
• I have added tests that prove my fix is effective or that my feature works
• New and existing unit tests pass locally with my changes
• Any dependent changes have been merged and published

Security Considerations

• This PR does not introduce any security concerns
• I have considered the security implications and addressed them

Screenshots (if applicable)

N/A

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[Copilot]

Pull request overview

This PR fixes a contradictory configuration in the com.shawnschwartz.cassh.rotate.plist LaunchAgent that controls hourly SSH key rotation. The plist had LaunchOnlyOnce=false with a comment claiming "Don't run if already running," but setting this key to false actually allows concurrent instances when the StartInterval timer fires.

Key changes:

• Removed the LaunchOnlyOnce key entirely to rely on launchd's default behavior
• Removed the misleading comment that contradicted the configuration

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[shawntz]

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