fix(ui): improve steps current step semantics

[wyf027]

Summary

• Add a default accessible name to the ordered steps list.
• Mark the active item with aria-current="step".
• Add screen-reader-only status text for completed, current, and upcoming steps.
• Hide decorative step numbers and connector lines from assistive technology.
• Add Steps tests for list naming, current step semantics, status text, and custom aria-label.
• Update Steps docs with accessibility behavior and StepItem API notes.

Gap Notes

• Ant Design Steps identifies current as the active step and documents status-driven step states: https://ant.design/components/steps/
• Element Plus Steps similarly models active progress through an active step and process/finish states: https://element-plus.org/en-US/component/steps
• MDN documents aria-current="step" for current items within a step indicator: https://developer.mozilla.org/en-US/docs/Web/Accessibility/ARIA/Reference/Attributes/aria-current

Validation

• npm ci
• npx prettier --write packages/ui/src/components/navigation/Steps/Steps.tsx packages/ui/src/components/navigation/Steps/Steps.test.tsx docs/components/steps.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 still reports 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.