fix: shrink the desktop balance card so history stays on screen

[o-mid]

Summary

• Portrait desktop windows were treated as mobile UI, so the balance card could grow to 768px and push transaction history off the page.
• Cap the desktop card at 320px (40% of width, whichever is smaller).

Fixes #3255

Test plan

• Linux / macOS / Windows: dashboard card is credit-card sized and history is visible without scrolling past a giant card
• Phone / narrow window: card still uses the existing mobile width

Made with Cursor

[RasheedAZ]

Is it possible to cap at a higher percentage of the screen width, say 70%, because 40% will be too small when it runs on Linux phones (open request #1393) which run 'desktop' apps.

Or maybe it can check if it's a small screen device...

hostnamectl status | grep Chassis gives: handset on Linux phones like Librem 5, FLX1s, etc.