Guest Channel (4th board / antenna ESP32)

Adds a 3rd audio output — an occasional Guest speaker — using the onboard-antenna ESP32 as the long-range A2DP source. I2C address 0x12, channel label "Guest" on the hub. No hardcoded speaker name: pick it via the hub (Guest -> pick -> scan -> select).

The antenna board is wired exactly like the other source boards — onto BOTH buses, plus common ground.

I2C control bus (to the hub)

Signal	Antenna board	goes to
SDA	GPIO32	shared SDA bus (hub GPIO15)
SCL	GPIO33	shared SCL bus (hub GPIO16)
GND	GND	common

Mind the orientation: GPIO32 = SDA, GPIO33 = SCL (do not swap). Pull-ups already on the bus. I2C address 0x12.

I2S audio bus (from Board A, the sink)

Signal	Antenna board (in)	from Board A (out)
BCK	GPIO19	GPIO5
WS	GPIO18	GPIO25
DATA	GPIO22	GPIO23
GND	GND	common

Common ground

All boards share one ground: antenna board + Board A + Headset + Speaker 1 + the S3 hub. Mandatory for both I2S and I2C.

Notes

The Guest is occasional: when no guest device is selected/present, the channel shows offline/idle on the hub — that's normal.
Antenna board is on the guest link on purpose: it's the furthest speaker, so it benefits most from the better antenna.