feat(web): premium visual redesign for POS prototype shell

[rmak78]

Summary

• execute a major visual redesign of web/index.html while preserving all existing screen IDs, hash routes, and navigation flows
• introduce a cleaner CSS architecture with design tokens (color/spacing/radius/shadows) and reusable utility-style component classes
• upgrade layout hierarchy, typography scale, spacing rhythm, card polish, and table presentation to feel production-grade
• improve visual semantics for status states (success/warning/danger), hover/active interactions, and overall dashboard readability

What stayed intact

• all section IDs (checkout, refunds, till-close, day-close, procurement, payroll)
• hash routing behavior and history.replaceState updates
• data-go button-based flow transitions and left-nav screen switching

Testing

• manually validated route transitions and screen title/description updates in-browser