Add full keyboard support and keyboard-based WiFi configuration for
M5Stack Cardputer Adv:
- TCA8418 I2C keyboard driver with 56-key matrix, interrupt-driven
key events, and debounce handling
- Keyboard WiFi config UI: scan/select/input SSID and password
directly on the device without needing a phone
- Volume control (up/down arrows) and brightness control (left/right)
via keyboard with fine-step adjustment near bounds
- Enter key to toggle chat state
- Display offset and backlight fixes for ST7789V2
- README with flash parameters and hardware specs
Co-authored-by: bot <bot@localhost>
