Add hardware-verified startup splash

[PurpleSentinel]

Summary

• add a Caterham startup splash sized for the 240x240 round display
• stream the native RGB565 asset into the existing framebuffer to avoid a second full-screen allocation
• preserve the text-only splash as a fallback when the image is missing or malformed
• retain the source artwork, preview, deterministic converter, and installation documentation

Root cause and colour handling

The first hardware build used the driver's misleading named colour mapping and cyclically exchanged the image channels. The converter now emits the big-endian RGB565 byte stream required by the GC9A01, with a primary-colour regression test covering the exact byte order.

Validation

• python3 -m unittest discover -s tests -v — 35 tests passed
• rendered successfully on the connected Waveshare RP2040-Touch-LCD-1.28
• user confirmed the corrected image colours on the physical display
• 93,552 bytes of heap remained free after loading and rendering the splash