Add hardware bill of materials

[PurpleSentinel]

What changed

• add a root-level hardware Bill of Materials
• identify the physical reference unit as Waveshare RP2040-Touch-LCD-1.28-B, SKU 26371
• document that the RP2040 board, touch display and CNC case are one product rather than separate BOM items
• list required installation items, optional battery requirements and integrated subsystems
• distinguish the reference unit from the uncased, non-touch, display-only, RP2350 and ESP32 variants
• link the BOM from the README and correct its reference-hardware wording

Why

Waveshare offers several similarly named 1.28-inch products. The previous README linked the uncased product-family page, which could lead a builder to buy the wrong physical variant or duplicate the processor, display and case as separate parts.

Sources

• official Waveshare RP2040-Touch-LCD-1.28-B product page
• official Waveshare RP2040-Touch-LCD-1.28 hardware wiki
• repository pin map and drivers for the supported display, touch controller and IMU

Validation

• python3 -m unittest discover -s tests — 185 tests pass
• git diff --check passes
• exact manufacturer part number, SKU, case construction, flash, IMU, battery connector and package contents verified against the current official product listing