Fix keyboard access for HQ detail modal and tracker stage movement

[akeight]

Closes #69

Summary

• Make HQ detail modal triggers keyboard-operable in deck cards, deck rows, and tracker cards (role="button", tabIndex, Enter/Space handlers, focus-visible styles).
• Upgrade DetailModal with dialog semantics (role="dialog", aria-modal, aria-labelledby), initial focus to close button, focus trapping, and focus restore to opener on close.
• Add keyboard-accessible tracker stage transition controls (previous/next stage buttons) as a fallback to drag-and-drop.

Why

Keyboard and assistive-technology users could not reliably open or stay within the details experience, and tracker stage movement required a mouse. This closes those accessibility gaps.

Test plan

• Tab to a deck card and press Enter/Space -> detail modal opens
• Tab to a deck list row and press Enter/Space -> detail modal opens
• Tab to a tracker card and press Enter/Space -> detail modal opens
• Screen reader announces modal as a dialog with title
• While modal is open, Tab/Shift+Tab cycles only inside dialog
• Escape closes modal
• Closing modal restores focus to the triggering element
• Use tracker prev/next stage buttons to move cards without drag-and-drop