Add project documentation

docs/decisions.md

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+# Project Decisions
+
+## Communications
+
+Primary:
+- RS-485
+
+Backup:
+- WiFi
+
+## Dashboard
+
+- Touchscreen only
+- No physical buttons required
+- Screen sleeps when ignition is off
+- Touch wakes display
+
+## Relay Design
+
+- ESP32 relay board does NOT switch loads directly
+- Bosch-style automotive relays switch all major loads
+
+## Power Loads
+
+Current:
+- Starlink
+- Fridge
+
+Future:
+- Inverter
+- Camp Lights
+
+## Sensors
+
+Current:
+- Fridge Zone 1
+- Fridge Zone 2
+- Rear Seat Area
+- Outside Air
+
+Future:
+- Battery Bay
+- Cabin Air
+- Water Tank
+
+## Configuration
+
+Configuration is stored on controller side, not browser side.
+
+## Logging
+
+No persistent logging currently planned.
+
+Focus:
+- Live monitoring
+- Alarms
+- Control