feat(ui): replace native select menus

[TWJohnJohn20116]

Summary

• replace all 10 native select elements with a shared themed dropdown component
• add selected-state checkmarks, responsive upward placement, and consistent light/dark styling
• support keyboard navigation, disabled items, click-outside closing, and accessible listbox semantics

Validation

• bun run check
• bun test (114 passed)
• bun run build