docs: prepare api contract for lilygo transition

docs/HARDWARE.md

@@ -213,3 +213,25 @@ Current expectation:
 - The Dashboard ESP32-S3 will consume temperature data from the Cargo ESP API.
 
 Do not move cargo/fridge temperature sensing to the dashboard controller unless the architecture is explicitly changed later.
+
+## Ordered Cargo ESP Hardware: LILYGO T-Relay-S3 6-Way
+
+The LILYGO T-Relay-S3 6-way board has been ordered as a future Cargo ESP candidate.
+
+Current active testing should continue on the existing 2-channel relay board until the LilyGO board arrives and is bench tested.
+
+Planned LilyGO role:
+
+    LILYGO T-Relay-S3 6-way
+            -> low-current control/relay outputs
+    WUPP 6-relay fused block
+            -> fused load switching
+    Fridge / Starlink / lights / spare / spare / spare
+
+Important guardrails:
+
+- Do not migrate active firmware assumptions until the board is physically available.
+- Bench test relay boot behavior before connecting to WUPP or vehicle loads.
+- Confirm relay polarity/state behavior.
+- Confirm available GPIO for DS18B20 and any optional OLED/status hardware.
+- Treat the LilyGO board as the controller, not the high-current load path.