docs: Update visual assets and improve documentation images

Visual Assets Updates:
- Updated ADC demonstration image (adc.png) with better clarity
- Enhanced I2C connection diagram (i2c.png) for better understanding
- Improved LED blink example visualization (led_blink.png)
- Updated RGB LED/NeoPixel diagram (neo.png) with clearer connections
- Enhanced SPI connection diagrams (sdcard.png, spi_external.png)
- Replaced pinout.png with pinout.jpg for better image quality and smaller file size

These visual improvements provide clearer guidance for hardware connections and enhance the overall documentation experience for ESP32-H2 development on PULSAR H2 board.

Author: GitHub Actions