feat(settings): show mesh discovery beacons

[Komzpa]

Adds provisional app-side support for the mesh discovery/config beacon discussed in meshtastic/firmware#7183 and meshtastic/firmware#10243, so companion apps can passively show the advertised mesh settings while the firmware protocol is still being shaped.

• Add a conservative fixed-width MeshDiscoveryBeacon decoder in core:model, gated to candidate discovery ports and accepting both sub-GHz and LORA_24 frequencies.
• Surface decoded beacons in the LoRa settings screen as passive nearby mesh settings.
• Decode candidate beacon payloads in debug logs for easier field testing.
• Keep this display-only: the app does not apply radio settings automatically.

Validation:

• JAVA_HOME=/usr/lib/jvm/java-21-openjdk-amd64 ANDROID_HOME=/usr/lib/android-sdk ./gradlew --no-daemon --no-configuration-cache :core:model:spotlessApply :core:model:jvmTest :feature:settings:compileKotlinJvm :core:model:spotlessCheck :feature:settings:spotlessCheck :core:resources:spotlessCheck
• codex review --base origin/main

Note: the full repo-wide spotlessApply was attempted first, but :core:barcode:spotlessKotlin hit a Maven Central TLS handshake while resolving io.github.oshai:kotlin-logging-jvm:7.0.7; the touched modules were then formatted and checked with scoped tasks.

[NomDeTom]

This probably needs protobufs to pull it all together across the protocol