fix(mqtt): size every client's buffers for a JWT CONNECT (F03)

Non-PSRAM boards allocated 512-byte MQTT buffers for non-JWT slots, so the
desired buffer size was a per-slot variable while the allocated size was fixed
at `esp_mqtt_client_init()`: IDF 4.4 does not resize those buffers in
`esp_mqtt_set_config()`, and the wrapper's own reassembly buffer is allocated
once for the client's lifetime. A slot reconfigured from non-JWT to JWT
therefore kept 512-byte buffers, and a valid JWT CONNECT (frame plus a 768-byte
token) could not fit — with no error naming the cause. Stopping and starting the
same handle could not change the capacity either.

Give every client 896 bytes on every board. The cost is 384 bytes per client on
a non-PSRAM board, which caps at 2 active slots, against a TLS handshake that
needs 16 KB of contiguous internal DRAM. In exchange the capacity transition
stops existing, so the reconfigure path never needs to recreate a client to grow
its buffers.

src/helpers/bridges/MQTTBridge.cpp

@@ -4674,15 +4674,23 @@ void MQTTBridge::optimizeMqttClientConfig(PsychicMqttClient* client, bool needs_
   // preserving at-least-once delivery while capping duplicates at one.
   client->setMessageRetransmitTimeout(15000);
 
-  // Buffer sizing: 896 is the minimum safe size for JWT clients (CONNECT + 768-byte JWT).
-  // On PSRAM boards, use a uniform size to reduce fragmentation from mixed allocations.
-  // On non-PSRAM boards, use smaller buffers for non-JWT slots to reduce heap usage and
-  // leave smaller holes during teardown/recreate cycles.
-#if defined(BOARD_HAS_PSRAM)
+  // Buffer sizing: 896 is the minimum safe size for a JWT CONNECT (frame plus a
+  // 768-byte token). Every client gets it, on every board.
+  //
+  // Non-PSRAM boards used to get 512 for non-JWT slots, which made the *desired*
+  // size a per-slot variable while the *allocated* size was fixed at client init
+  // — IDF 4.4 allocates the MQTT buffers in esp_mqtt_client_init() and
+  // esp_mqtt_set_config() does not resize them, and the wrapper's own reassembly
+  // buffer is likewise allocated once (F03). A slot reconfigured from non-JWT to
+  // JWT therefore kept 512-byte buffers and its valid CONNECT could not fit,
+  // with no error that named the cause. Sizing every client for the largest
+  // CONNECT it might ever have to send removes the transition entirely.
+  //
+  // The cost is 384 bytes per client on a non-PSRAM board (at most 2 active
+  // slots there), against a handshake that needs 16 KB of *contiguous* internal
+  // DRAM — noise, and it buys the removal of a recreate case.
   static const int MQTT_CLIENT_BUFFER_SIZE = 896;
-#else
-  const int MQTT_CLIENT_BUFFER_SIZE = needs_large_buffer ? 896 : 512;
-#endif
+  (void)needs_large_buffer;   // kept: callers still express the intent
 
   client->setBufferSize(MQTT_CLIENT_BUFFER_SIZE);