refactor: Replace Moshi with kotlinx.serialization

Remove Moshi dependency entirely, completing the migration to kotlinx.serialization. All JSON serialization now uses kotlinx with explicit @SerialName annotations for wire format stability.

- Migrate PodDeviceCache from Moshi to kotlinx Json injection

- Add MapIntByteArrayBase64Serializer for BleScanResult cache compat

- Strip @JsonClass/@Json annotations from all dual-annotated classes

- Delete Moshi adapters, ProGuard rules, and build config

- Convert compat tests to pure kotlinx round-trip tests

buildSrc/src/main/java/Dependencies.kt

@@ -60,11 +60,6 @@ fun DependencyHandlerScope.addDagger() {
     kspAndroidTest("com.google.dagger:hilt-android-compiler:${Versions.Dagger.core}")
 }
 
-fun DependencyHandlerScope.addMoshi() {
-    implementation("com.squareup.moshi:moshi:1.15.2")
-    implementation("com.squareup.moshi:moshi-adapters:1.15.2")
-    add("ksp", "com.squareup.moshi:moshi-kotlin-codegen:1.15.2")
-}
 
 fun DependencyHandlerScope.addOkio() {
     implementation("com.squareup.okio:okio:3.1.0")