Add S3 hub I2C control-bus wiring

Hub-Control-Bus-%28I2C%29.md

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+# Hub Control Bus (I2C)
+
+Wires the **ESP32-S3-Touch-LCD-1.28 hub** to the two source boards (B = JBL,
+C = Cardo) so the on-screen UI can set delay / volume (and later pick speakers).
+
+## S3 expansion header — free pins
+The 1.27 mm header (P2) brings out: **GPIO15, 16, 17, 18, 21, 33** + **3V3**, **VSYS**, **GND**.
+We use two of them for I2C.
+
+## I2C bus wiring (3 wires + pull-ups)
+
+| Signal | S3 hub (master) | Board B (JBL) | Board C (Cardo) |
+|--------|-----------------|---------------|-----------------|
+| SDA    | **GPIO15**      | GPIO32        | GPIO32          |
+| SCL    | **GPIO16**      | GPIO33        | GPIO33          |
+| GND    | **GND** (header)| GND           | GND             |
+
+- S3 **GPIO15 (SDA)** -> B **GPIO32** *and* C **GPIO32**
+- S3 **GPIO16 (SCL)** -> B **GPIO33** *and* C **GPIO33**
+- S3 **GND** -> common with B and C (and with Board A — everything shares one ground)
+
+### Pull-up resistors (required for I2C)
+Add **two ~4.7 kohm resistors**: one from **SDA -> 3V3**, one from **SCL -> 3V3**
+(use the S3 header's 3V3 pin). One pair for the whole bus is enough.
+
+## I2C addresses
+- Board B (JBL)   = **0x10**
+- Board C (Cardo) = **0x11**
+
+## Notes
+- This is separate from the audio I2S bus (Board A GPIO5/25/23 -> B/C GPIO19/18/22).
+- B/C touch pads (GPIO4 = +, GPIO27 = -) still work as a local fallback.
+- Keep wires short; common ground across all boards is mandatory.
+- The S3 is powered by its own USB/battery; only GND is shared for signaling.