feat: polish, accessibility, and internationalization

[mairas]

Description

Ensure UI meets Cockpit standards for accessibility, internationalization, and overall polish.

Implementation Requirements

MANDATORY: Follow docs/IMPLEMENTATION_CHECKLIST.md

Implementation Details

1. Accessibility audit: Keyboard accessible, tab order, ARIA labels, live regions, focus indicators, contrast
2. Internationalization: All strings use cockpit.gettext(), translation comments, RTL considered
3. Mobile responsiveness: Small screens, touch targets, scaling, no horizontal scroll
4. Loading states: Spinners, progress, skeletons, clear indications
5. Polish items: Smooth transitions, consistent spacing, helpful tooltips, inline validation
6. Error messages: Clear, actionable, avoid jargon, suggest solutions

Acceptance Criteria

• WCAG 2.1 AA compliance
• All strings internationalized
• Mobile-responsive
• Loading/empty states polished
• Error messages helpful
• Matches Cockpit quality standards

Dependencies

• All feature tasks (feat: WiFi device detection and basic UI structure #2-feat: simultaneous AP + Client mode #8)