docs(gateway): update diagrams following review feedback

- Simplify class diagram: remove KEY_* constants, add is_duplicate
  and on_disconnect, keep only behavior-relevant elements
- Update sequence diagram: replace repeated conditions with else,
  add deduplication step, update payload size to 14 bytes

doc_resources/gateway/class_diagram.puml

@@ -1,30 +1,31 @@
 @startuml
 skinparam linestyle ortho
+
 class Gateway {
     - gateway_id: str
     - mqtt_broker: str
     - mqtt_port: int
     - mqttc: MQTTClient
     --
-    + KEY_WINDOW: 0x01
-    + KEY_HUMIDITY: 0x02
-    + KEY_TEMP: 0x03
-    + KEY_CO2: 0x04
-    + KEY_BATTERY: 0x05
-    + INVALID_VALUE: 0xFFFFFFFF
     + EXPECTED_PAYLOAD_SIZE: 14
+    + DEDUP_WINDOW_SECONDS: 10
+    + INVALID_VALUE: 0xFFFFFFFF
     --
     + decode_payload(data: bytes): dict
     + publish(mac: str, data: dict)
+    + is_duplicate(mac: str): bool
     + on_device_found(device, adv_data)
-    + on_connect(client, userdata, flags, reason_code, properties)
-    + on_publish(client, userdata, mid, reason_code, properties)
+    + on_connect(...)
+    + on_disconnect(...)
+    + on_publish(...)
     + run()
 }
+
 class BleakScanner {
     + start()
     + stop()
 }
+
 class MQTTClient {
     + connect()
     + publish()
@@ -32,6 +33,8 @@ class MQTTClient {
     + username_pw_set()
     + loop_start()
 }
+
 Gateway o-- BleakScanner
 Gateway o-- MQTTClient
+
 @enduml

doc_resources/gateway/sequence_data_collection.puml

@@ -11,7 +11,7 @@ thingy -> gw : BLE advertising packet
 
 alt company_id != 0xffff
     gw -> gw : discard packet
-else company_id == 0xffff
+else
     gw -> gw : check payload size
 
     alt payload size != 14 bytes
@@ -21,15 +21,19 @@ else company_id == 0xffff
 
         alt unknown key in payload
             gw -> gw : discard packet\nlog debug
-        else valid keys
+        else
             alt CO2 == 0xFFFFFFFF
                 gw -> gw : discard CO2 value\n(sensor not ready)
             end
 
-            gw -> gw : add UTC timestamp
-            gw -> broker : publish JSON\n{gateway_id}/{mac}/update
-            broker --> gw : on_publish confirmed
-            broker -> db : store measurement
+            alt duplicate within 10 seconds
+                gw -> gw : discard packet\n(deduplication)
+            else
+                gw -> gw : add UTC timestamp
+                gw -> broker : publish JSON\n{gateway_id}/{mac}/update
+                broker --> gw : on_publish confirmed
+                broker -> db : store measurement
+            end
         end
     end
 end