Align GitHub workflow detection

[GreyforgeLabs]

Summary

• Make github status, github install, and github uninstall identify Cortex-owned workflows with the existing cortex github install generator marker.
• Prevent github install from silently creating Cortex.yml when another generated Cortex workflow already exists under a different filename.
• Let github uninstall remove the same generated workflow that github status reports, even when it is named release.yml.
• Add a CLI regression covering status, duplicate install rejection, and uninstall against a generated release.yml.

Fixes PlatformNetwork/bounty-challenge#53318.
Also addresses PlatformNetwork/bounty-challenge#53317.

Validation

• cargo test -p cortex-cli --test github_workflow_detection --no-default-features --features cortex-tui -- --nocapture
• cargo check -p cortex-cli --no-default-features --features cortex-tui
• cargo fmt --package cortex-cli --check
• git diff --check

[greptile-apps]

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