Introduce pluggable hardware profiles for additional boards

[PurpleSentinel]

Parent: #23

Summary

Separate board pin maps and capabilities so the standalone Waveshare display or future RP2040 variants can be supported without destabilizing the current integrated board.

Acceptance criteria

• Move pin assignments and optional capabilities into explicit profiles.
• Select the profile safely at build, install, or boot time.
• Reject incompatible profiles with a clear diagnostic.
• Keep the current integrated board as the tested default.
• Add profile validation tests and hardware-specific installation documentation.

Roadmap group

Sensors, power, and hardware expansion