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/JsonGeneratorExample/JsonGeneratorExample.ino

@@ -0,0 +1,65 @@
+// ArduinoJson - https://arduinojson.org
+// Copyright © 2014-2026, Benoit BLANCHON
+// MIT License
+//
+// This example shows how to generate a JSON document with ArduinoJson.
+//
+// https://arduinojson.org/v7/example/generator/
+
+#include <ArduinoJson.h>
+
+void setup() {
+  // Initialize Serial port
+  Serial.begin(9600);
+  while (!Serial)
+    continue;
+
+  // Allocate the JSON document
+  JsonDocument doc;
+
+  // Add values in the document
+  doc["sensor"] = "gps";
+  doc["time"] = 1351824120;
+
+  // Add an array
+  JsonArray data = doc["data"].to<JsonArray>();
+  data.add(48.756080);
+  data.add(2.302038);
+
+  // Generate the minified JSON and send it to the Serial port
+  serializeJson(doc, Serial);
+  // The above line prints:
+  // {"sensor":"gps","time":1351824120,"data":[48.756080,2.302038]}
+
+  // Start a new line
+  Serial.println();
+
+  // Generate the prettified JSON and send it to the Serial port
+  serializeJsonPretty(doc, Serial);
+  // The above line prints:
+  // {
+  //   "sensor": "gps",
+  //   "time": 1351824120,
+  //   "data": [
+  //     48.756080,
+  //     2.302038
+  //   ]
+  // }
+}
+
+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
+// serialization problem.
+//
+// The book "Mastering ArduinoJson" contains a tutorial on serialization.
+// It begins with a simple example, like the one above, and then adds more
+// features like serializing directly to a file or an HTTP request.
+// Learn more at https://arduinojson.org/book/
+// Use the coupon code TWENTY for a 20% discount ❤❤❤❤❤