fix(map): apply kotlinx-serialization compiler plugin to androidApp

[jamesarich]

Problem

Crashlytics is reporting a runtime crash in the latest build:

kotlinx.serialization.SerializationException: Serializer for class 'CustomTileProviderConfig' is not found.
Please ensure that class is marked as '@Serializable' and that the serialization compiler plugin is applied.
  ...
  kotlinx.serialization.json.Json.encodeToString(Json.java:205)
  org.meshtastic.app.map.repository.CustomTileProviderRepositoryImpl$saveDataToPrefs$2.invokeSuspend(CustomTileProviderRepository.kt:97)

Root cause

The class is annotated @Serializable — this is not a missing annotation, nor an R8/minification issue. The androidApp module pulled in the kotlinx-serialization runtime (kotlinx-serialization-json) but never applied the compiler plugin (org.jetbrains.kotlin.plugin.serialization).

Without the compiler plugin, @Serializable is inert — no $serializer is synthesized. The code still compiles (the annotation and Json resolve from the runtime lib), but Json.encodeToString falls back to a reflective serializer lookup at runtime, finds nothing, and throws the exception above. Note the tail of the message: "…and that the serialization compiler plugin is applied."

Every other module that serializes (16 of them across core/* and feature/*) applies the shared meshtastic.kotlinx.serialization convention plugin. androidApp was the lone exception. The bug only surfaced now because the custom-tile-provider save path is rarely exercised — it would crash in debug too.

MapCameraPosition (also @Serializable in androidApp) had the same latent bug.

Fix

Apply the existing meshtastic.kotlinx.serialization convention plugin to androidApp, exactly as the other serializing modules do. The convention plugin adds serialization-core when kotlin.android is present (composes cleanly with the existing serialization-json dep) and applies the compiler plugin so $serializer classes are generated for all @Serializable types in the module.

Verification

• ./gradlew spotlessCheck detekt :androidApp:assembleGoogleDebug — pass (the affected classes live in src/google)

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