Fix Arduino compilation errors: ArduinoJson v7 type and missing constant

Co-authored-by: dorkmo <[email protected]>

Author: Copilot

TankAlarm-112025-Client-BluesOpta/TankAlarm-112025-Client-BluesOpta.ino

@@ -1446,7 +1446,7 @@ static void applyConfigUpdate(const JsonDocument &doc) {
       }
       // Handle per-relay momentary durations (in seconds)
       if (t.containsKey("relayMomentaryDurations")) {
-        JsonArray durations = t["relayMomentaryDurations"].as<JsonArray>();
+        JsonArrayConst durations = t["relayMomentaryDurations"].as<JsonArrayConst>();
         for (size_t r = 0; r < 4 && r < durations.size(); r++) {
           uint16_t dur = durations[r].as<uint16_t>();
           // Enforce minimum of 1 second, max of 86400 (24 hours)

TankAlarm-112025-Server-BluesOpta/TankAlarm-112025-Server-BluesOpta.ino

@@ -104,6 +104,10 @@
 #define MAX_TANK_RECORDS 32
 #endif
 
+#ifndef MAX_TANKS
+#define MAX_TANKS 8  // Maximum tanks per client device (must match client configuration)
+#endif
+
 #ifndef MAX_EMAIL_BUFFER
 #define MAX_EMAIL_BUFFER 2048
 #endif