Add configurable display and gesture rotation

[PurpleSentinel]

Summary

• add persisted 0, 90, 180, and 270 degree clockwise mount rotation
• counter-rotate the GC9A01 display while mapping CST816T gestures to the viewer's directions
• add a live Settings preview with save and safe cancellation
• migrate existing user settings to a 0 degree default and reset rotation with Restore Defaults
• document configuration and installation changes

Impact

The timer can now be mounted in any quarter-turn orientation without sideways text or confusing directional gestures. Existing installations retain their settings and gain the native 0 degree orientation automatically.

Validation

• python -m unittest discover -s tests -v — 125 tests passed
• all four controller mappings, gesture mappings, persistence paths, cancellation, and circular menu layouts covered on the host
• firmware uploaded to the connected Waveshare RP2040 board and booted successfully on MicroPython 1.21.0

Closes#33