Refactor selectors to modal-based UI

[yimsk]

Summary

ProfileSelector, RegionSelector, and HelpView should be displayed as modals instead of full-screen views for better UX consistency.

Current Behavior

Component	Display	q behavior
ProfileSelector	Full-screen view (viewStack push)	Esc to go back
RegionSelector	Full-screen view (viewStack push)	Esc to go back
HelpView	Full-screen view	Esc to go back
ProfileDetailView	Modal (overlay)	q/Esc/d to close
ActionMenu	Modal	Esc to close

Proposed Change

Convert ProfileSelector, RegionSelector, and HelpView to modal-based display:

• Background remains visible (dimmed)
• q closes the modal naturally
• Consistent behavior across all overlay-style UIs

Benefits

• Better context retention (see underlying view while selecting)
• Consistent q to close behavior
• Unified modal pattern across the app

Tasks

• Refactor ProfileSelector to modal
• Refactor RegionSelector to modal
• Refactor HelpView to modal
• Update app.go view display logic
• Adjust MultiSelector sizing for modal context

[yimsk]

Implemented in PR #84