fix(ui): improve time picker accessibility

[wyf027]

Summary

• Add accessible combobox trigger semantics to TimePicker with aria-expanded, aria-controls, and aria-haspopup.
• Support keyboard opening and Escape closing from the trigger.
• Render hour and minute values as native buttons inside an accessible popup panel.
• Add focused Vitest coverage for trigger semantics, keyboard behavior, selection, and disabled state.

Verification

• npx prettier --write packages/ui/src/components/form/pickers/TimePicker/TimePicker.tsx packages/ui/src/components/form/pickers/TimePicker/TimePicker.test.tsx
• npx vitest run src/components/form/pickers/TimePicker/TimePicker.test.tsx
• npx eslint src/components/form/pickers/TimePicker/TimePicker.tsx src/components/form/pickers/TimePicker/TimePicker.test.tsx
• git diff --check
• npm run lint:ui
• npm run typecheck:ui
• npm run test:ui
• npm run build

Notes

• npm install reported existing audit findings: 1 low, 4 moderate, 2 high. No dependency changes are included in this PR.