Increase live countdown font size

[PurpleSentinel]

Summary

• increase the live track and rest countdown from the 64-pixel font to the 74-pixel native font
• apply the larger size consistently to normal, warning, expiry, overrun, and rest frames
• document why 74 pixels is the nearest available pre-rendered size to a 10% increase

Why

The running countdown is the most important information to read at a glance while driving. A target 10% increase from 64 pixels is 70.4 pixels; the available native sizes are 64 and 74 pixels, making 74 the nearest option.

Impact

The countdown is 15.6% larger and more legible while remaining centered within the 240x240 circular display. The elapsed time retains its existing size and separation.

Validation

• python -m unittest discover -s tests -v - 69 tests passed
• tests verify nearest native-size selection and every live display state
• maximum-width 60:00 geometry is checked against the circular display edges
• rendered and captured the production framebuffer on the connected Waveshare RP2040-Touch-LCD-1.28
• visually confirmed centering, circular margin, and elapsed-time separation