fix(ui): improve upload keyboard accessibility

[wyf027]

Summary

• Keep the Upload file input in the accessibility tree by using a visually hidden sr-only input instead of display: none.
• Add a visible focus ring on the upload trigger through Tailwind peer-focus-visible classes.
• Add list semantics for the controlled file list.
• Add Upload tests for label association, keyboard focus, file metadata changes, disabled/native attributes, and file list semantics.
• Document keyboard behavior plus missing disabled and triggerText props.

Gap Notes

• Ant Design Upload documents native accept, multiple, disabled, and controlled fileList behavior: https://ant.design/components/upload/
• Element Plus Upload exposes disabled and file-list patterns around its trigger and upload list: https://element-plus.org/en-US/component/upload.html
• MDN documents <input type="file"> as the native file selection control: https://developer.mozilla.org/en-US/docs/Web/HTML/Reference/Elements/input/file
• Nova UI previously used Tailwind hidden on the file input, so keyboard users could not tab to the native picker control.

Validation

• npx prettier --write packages/ui/src/components/form/controls/Upload/Upload.tsx packages/ui/src/components/form/controls/Upload/Upload.test.tsx docs/components/upload.md
• npm run lint:ui
• npm run typecheck:ui
• npm run test:ui (24 files, 74 tests)
• npm run build:ui
• npm run build

Notes

• npm ci completed with existing Node 23 engine warnings and existing npm audit findings (1 low, 4 moderate, 2 high).
• npm run build still reports existing Browserslist and VitePress chunk-size warnings.

[ecc-tools]

ECC bundle files are already tracked in this repository. Skipping generation of another bundle PR.