Firmware improvements: Input VIN gating, fast parallel calibration, and smooth non-blocking LED animations

[napowderly]

Summary

• Add input-voltage sensing on IO16 and block startup until VIN is stable between 11–13 V.
• Replace per-cell sequential calibration with a fast parallel routine.
• Add smooth, non-blocking LED animations via a dedicated FreeRTOS task (breathing red for VIN wait, full-strip progress bar for calibration).
• Add GETVIN UART command and switch CALIBRATE_ALL to use the fast method.

Motivation

• Prevent bringing up the system on bad or unstable input power.
• Cut calibration time by broadcasting DAC setpoints to all cells, settling once, and reading all cells in a batch.
• Keep LED feedback smooth and responsive during blocking operations.