"Design a lightweight, ultra-thin cellular-gateway companion slate running on an ESP32-S31 MCU. The project is a low-latency voice-interaction terminal and e-book reader syncing text and audio with an iPhone backend.
Core constraints:
Target PCB thickness: 0.8mm (4-layer stackup).
All active components must be constrained to the Top Layer only to keep the bottom completely flat for a pouch battery.
Optimize component selection for low-profile, surface-mount parts available in the JLCPCB/LCSC library.
Please generate a block diagram and a system layout plan containing four primary functional blocks:
Core Processing (ESP32-S31 + Flash/PSRAM)
Power Management (Mid-mount USB-C, LiPo charging via TP4056, 3.3V LDO regulation, and Battery Fuel Gauge tracking)
I2S Audio Pipeline (MEMS Microphone + MAX98357A I2S Audio Amplifier)
High-Speed SPI Display and Capacitive Touch Screen interface."