proposal: OTA for Zigbee and BLE

[mishan]

I have created a proposal for a plan to implement OTA (both Zigbee and BLE) for the AirCube and AirCube Pro.

Disclosure: this proposal was created with the assistance of AI (Opus 5).
Linked issue: #63

tl;dr / things to call out:

• OTA requires having two slots for the firmware
• We can size down the firmware just enough with simple compile time optimizations
• If needed, we can get more space for the firmware images through various means, but there are caveats
• Need to make a call whether to do signed OTA updates for BLE as it affects firmware size
• Zigbee is going to need a manufacturer code for the OTA updates
• Zigbee OTA updates might be very slow due to the larger firmware, and they could have issues. This should be tested as early on as possible in the dev process.

[mishan]

@StuckAtPrototype btw, I am happy to work on this once you've signed off on this and have decided on details like whether to go ahead with the signed updates for BLE