Handle unavailable touch and IMU hardware

[PurpleSentinel]

Summary

• classify peripheral I2C failures and unexpected chip identities
• retry transient touchscreen initialization failures before a controlled, actionable stop
• initialize the QMI8658 only when Launch Mode needs it and fall back to normal timing when it is unavailable
• handle launch-time IMU read failures without crashing
• document the peripheral failure policy and deployment requirements

Root cause

The QMI8658 driver returned an undefined NULL value for an unexpected chip ID, the touch driver could return a partially initialized object, and startup constructed the IMU even when Launch Mode was disabled. Missing or incompatible hardware could therefore produce undefined-name errors or later crashes.

Impact

The required touchscreen now either initializes completely or stops safely after bounded retries. The optional IMU can fail without preventing standard swipe-down timing, while serial and on-screen messages explain the hardware problem.

Validation

• python -m unittest discover -s tests -v - 59 tests passed
• deployed and boot-tested on the connected Waveshare RP2040-Touch-LCD-1.28
• detected CST816T revision 1 and QMI8658 revision 124
• verified clean startup with saved Launch Mode sensitivity 0.5

Closes #11