Recreate release timeline header with scrollable controls

[unclehowell]

Summary

• replace the previous range input slider with a scrollable release stage button track tied to the existing popups
• add a cascading dropdown/back control ahead of the timeline that hides and restores the primary menu as selections are made
• restyle the top release header to support horizontal scrolling and highlight the active stage when clicked or navigated by keyboard

Testing

• not run (not requested)

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Codex Task