CUB-230: ESP32 offline status buffering and replay on reconnect

- Add SPIFFS buffer for status entries when MQTT offline
- FIFO eviction when max_buffer_entries exceeded
- Replay buffer on MQTT reconnect
- Configurable buffer size in esp32-config.json

firmware/.pio/libdeps/esp32-mqtt/ArduinoJson/examples/JsonParserExample/JsonParserExample.ino

@@ -0,0 +1,65 @@
+// ArduinoJson - https://arduinojson.org
+// Copyright © 2014-2026, Benoit BLANCHON
+// MIT License
+//
+// This example shows how to deserialize a JSON document with ArduinoJson.
+//
+// https://arduinojson.org/v7/example/parser/
+
+#include <ArduinoJson.h>
+
+void setup() {
+  // Initialize serial port
+  Serial.begin(9600);
+  while (!Serial)
+    continue;
+
+  // Allocate the JSON document
+  JsonDocument doc;
+
+  // JSON input string.
+  const char* json =
+      "{\"sensor\":\"gps\",\"time\":1351824120,\"data\":[48.756080,2.302038]}";
+
+  // Deserialize the JSON document
+  DeserializationError error = deserializeJson(doc, json);
+
+  // Test if parsing succeeds
+  if (error) {
+    Serial.print(F("deserializeJson() failed: "));
+    Serial.println(error.f_str());
+    return;
+  }
+
+  // Fetch the values
+  //
+  // Most of the time, you can rely on the implicit casts.
+  // In other case, you can do doc["time"].as<long>();
+  const char* sensor = doc["sensor"];
+  long time = doc["time"];
+  double latitude = doc["data"][0];
+  double longitude = doc["data"][1];
+
+  // Print the values
+  Serial.println(sensor);
+  Serial.println(time);
+  Serial.println(latitude, 6);
+  Serial.println(longitude, 6);
+}
+
+void loop() {
+  // not used in this example
+}
+
+// See also
+// --------
+//
+// https://arduinojson.org/ contains the documentation for all the functions
+// used above. It also includes an FAQ that will help you solve any
+// deserialization problem.
+//
+// The book "Mastering ArduinoJson" contains a tutorial on deserialization.
+// It begins with a simple example, like the one above, and then adds more
+// features like deserializing directly from a file or an HTTP request.
+// Learn more at https://arduinojson.org/book/
+// Use the coupon code TWENTY for a 20% discount ❤❤❤❤❤