⚡ Improve QR code layout for narrow screens (#4012)

[guiyanakuang]

Closes #4012

Summary

• Remove weight(1f) from QR container — content flows naturally with Arrangement.Center
• Move BoxWithConstraints to outer level, compute QR size as ~65% of available width (120–320dp range)
• Add verticalScroll for small screen safety
• Simplify bottom section by flattening nested Column/Box wrappers
• Use success.color for Verified_user icon tint
• Adjust spacing for tighter, more natural grouping on narrow screens

Test plan

• Verify QR code layout looks good on desktop (~440dp content width)
• Verify layout is compact on narrow phone screens (~360dp)
• Verify all content visible and scrollable on very small screens
• Verify QR code remains scannable at all sizes