Enhanced MQTT support with separate topics and multipliers (#173)

- Add separate MQTT topics for power, energy, and state monitoring
  - mqtt_power_topic, mqtt_power_path, mqtt_power_multiplier
  - mqtt_energy_topic, mqtt_energy_path, mqtt_energy_multiplier
  - mqtt_state_topic, mqtt_state_path, mqtt_state_on_value
- Support different MQTT topics per data type (e.g., Zigbee2MQTT with
  separate power/energy/state topics)
- Individual multipliers for power and energy (e.g., mW→W, Wh→kWh)
- Configurable ON value for state monitoring (e.g., "ON", "true", "1")
- Maintain backward compatibility with legacy mqtt_topic/mqtt_multiplier
- Database migration auto-copies legacy fields to new fields
- Update backup/restore to handle new MQTT fields
- Add backend tests for new MQTT configurations
- Update frontend form with organized Power/Energy/State sections

Closes #173

backend/app/models/smart_plug.py

@@ -25,13 +25,30 @@ class SmartPlug(Base):
     ha_energy_total_entity: Mapped[str | None] = mapped_column(String(100), nullable=True)  # sensor.xxx_total
 
     # MQTT plug fields (required when plug_type="mqtt")
+    # Legacy field - kept for backward compatibility, now use mqtt_power_topic
     mqtt_topic: Mapped[str | None] = mapped_column(
         String(200), nullable=True
-    )  # e.g., "zigbee2mqtt/shelly-working-room"
+    )  # e.g., "zigbee2mqtt/shelly-working-room" (deprecated, use mqtt_power_topic)
+
+    # Power monitoring
+    mqtt_power_topic: Mapped[str | None] = mapped_column(String(200), nullable=True)  # Topic for power data
     mqtt_power_path: Mapped[str | None] = mapped_column(String(100), nullable=True)  # e.g., "power_l1" or "data.power"
+    mqtt_power_multiplier: Mapped[float] = mapped_column(Float, default=1.0)  # Unit conversion for power
+
+    # Energy monitoring
+    mqtt_energy_topic: Mapped[str | None] = mapped_column(String(200), nullable=True)  # Topic for energy data
     mqtt_energy_path: Mapped[str | None] = mapped_column(String(100), nullable=True)  # e.g., "energy_l1"
+    mqtt_energy_multiplier: Mapped[float] = mapped_column(Float, default=1.0)  # Unit conversion for energy
+
+    # State monitoring
+    mqtt_state_topic: Mapped[str | None] = mapped_column(String(200), nullable=True)  # Topic for state data
     mqtt_state_path: Mapped[str | None] = mapped_column(String(100), nullable=True)  # e.g., "state_l1" for ON/OFF
-    mqtt_multiplier: Mapped[float] = mapped_column(Float, default=1.0)  # Unit conversion (e.g., 0.001 for mW→W)
+    mqtt_state_on_value: Mapped[str | None] = mapped_column(
+        String(50), nullable=True
+    )  # What value means "ON" (e.g., "ON", "true", "1")
+
+    # Legacy multiplier - kept for backward compatibility
+    mqtt_multiplier: Mapped[float] = mapped_column(Float, default=1.0)  # Deprecated, use mqtt_power_multiplier
 
     # Link to printer (1:1)
     printer_id: Mapped[int | None] = mapped_column(