Organize firmware into dedicated directories

[PurpleSentinel]

Summary

• move the flat MicroPython payload into a dedicated firmware/ directory
• move maintained documentation into docs/
• add a layout-aware deployment tool that installs the firmware flat on the device and preserves existing user settings
• update CI, tests, asset tools, and repository documentation for the new paths
• add regression coverage that prevents runtime files drifting back into the repository root

Why

The repository root mixed device source, generated runtime assets, configuration, and documentation. The new layout makes the project easier to navigate and maintain without changing the Pico's required flat filesystem or sibling imports.

Impact

Deployments should now use python tools/deploy.py. By default it preserves the device's user.json, copies support files first, installs main.py last, and resets the board.

Validation

• python3 -m compileall -q firmware tests tools
• python3 -m unittest discover -s tests -t . — 189 tests pass
• git diff --check
• deployed through the new tool to the connected Waveshare device
• confirmed flat device filesystem, retained user settings, and successful boot into Timer mode