feat(mqtt): add CONFIG_MESHTASTIC_DEFAULT_OK_TO_MQTT seed

Nothing set config.lora.config_ok_to_mqtt, so the consent bit the previous
commit added could only ever be false without a phone-app or admin write.

Seed it from Kconfig, defaulting to n to match the reference. Consent to
having your traffic carried off the local RF mesh and onto a broker — possibly
a public one — should be opt-in, so the shared default stays off and a
deployment that wants it enables it locally.

This governs only our OWN traffic. Whether this node republishes other
people's packets is decided by their bit and by whether the broker is private,
which is the other half and unchanged here.

Author: roperscrossroads

src/Kconfig.core

@@ -115,6 +115,24 @@ config MESHTASTIC_DEFAULT_REGION
 
 	  A US device needs no licence: 902-928 MHz is unlicensed ISM spectrum.
 
+config MESHTASTIC_DEFAULT_OK_TO_MQTT
+	bool "Consent to our traffic being republished to MQTT by default"
+	default n
+	help
+	  Seeds config.lora.config_ok_to_mqtt on first boot. When set, every
+	  packet this node originates carries the OK_TO_MQTT bit, telling any
+	  gateway that hears it that our traffic may be republished to an MQTT
+	  broker — including a public one.
+
+	  Defaults to n, matching the reference firmware: consent to being
+	  rebroadcast off the local RF mesh should be opt-in.
+
+	  This governs only OUR OWN traffic. Whether this node republishes other
+	  people's packets is a separate matter, decided by their bit and by
+	  whether the configured broker is private.
+
+	  A later admin or phone-app change overrides this seed.
+
 config MESHTASTIC_TX_POWER
 	int "Default TX power (dBm)"
 	default 17

src/meshtastic_config_store.c

@@ -415,6 +415,8 @@ static void seed_config_defaults(const struct meshtastic_config *cfg)
 
 	idx = index_for_config_tag(meshtastic_Config_lora_tag);
 	store.configs[idx].payload_variant.lora.use_preset = true;
+	store.configs[idx].payload_variant.lora.config_ok_to_mqtt =
+		IS_ENABLED(CONFIG_MESHTASTIC_DEFAULT_OK_TO_MQTT);
 	store.configs[idx].payload_variant.lora.modem_preset =
 		meshtastic_Config_LoRaConfig_ModemPreset_LONG_FAST;
 	/* Declared, not inferred. The region used to be derived from the