feat(shared): add shared module with common DTO models

New Gradle module :shared (pure Kotlin/JVM) containing @Serializable
DTO classes for use by both the Android app and future Ktor server.

shared/src/main/kotlin/de/krisenvorrat/shared/model/:
- InventoryDto: root DTO replacing ExportData (version, categories,
  locations, items, settings)
- CategoryDto, LocationDto, ItemDto, SettingDto: extracted from
  the former *Export data classes in :app

Migration in :app:
- ExportData.kt deleted (classes moved to :shared)
- ImportExportRepositoryImpl now imports from de.krisenvorrat.shared.model
- app/build.gradle.kts adds implementation(project(:shared))

Build config:
- libs.versions.toml: added kotlin-jvm plugin entry
- build.gradle.kts (root): registered kotlin-jvm plugin
- settings.gradle.kts: include(:shared)

JSON wire format is unchanged; all 165 existing tests pass.

Closes #39

app/build.gradle.kts

@@ -71,6 +71,9 @@ dependencies {
     // Serialization
     implementation(libs.kotlinx.serialization.json)
 
+    // Shared module
+    implementation(project(":shared"))
+
     testImplementation(libs.junit)
     testImplementation(libs.kotlinx.coroutines.test)
     testImplementation(libs.mockk)

app/src/main/java/de/krisenvorrat/app/data/export/ExportData.kt

@@ -1,49 +0,0 @@
-package de.krisenvorrat.app.data.export
-
-import kotlinx.serialization.EncodeDefault
-import kotlinx.serialization.ExperimentalSerializationApi
-import kotlinx.serialization.Serializable
-
-@OptIn(ExperimentalSerializationApi::class)
-@Serializable
-internal data class ExportData(
-    @EncodeDefault(EncodeDefault.Mode.ALWAYS) val version: Int = 1,
-    val categories: List<CategoryExport>,
-    val locations: List<LocationExport>,
-    val items: List<ItemExport>,
-    val settings: List<SettingExport>
-)
-
-@Serializable
-internal data class CategoryExport(
-    val id: Int,
-    val name: String
-)
-
-@Serializable
-internal data class LocationExport(
-    val id: Int,
-    val name: String
-)
-
-@Serializable
-internal data class ItemExport(
-    val id: String,
-    val name: String,
-    val categoryId: Int,
-    val quantity: Double,
-    val unit: String,
-    val unitPrice: Double,
-    val kcalPer100g: Int?,
-    val expiryDate: String?,
-    val locationId: Int,
-    val minStock: Double,
-    val notes: String,
-    val lastUpdated: Long
-)
-
-@Serializable
-internal data class SettingExport(
-    val key: String,
-    val value: String
-)

app/src/main/java/de/krisenvorrat/app/data/export/ImportExportRepositoryImpl.kt

@@ -9,6 +9,11 @@ import de.krisenvorrat.app.data.db.entity.ItemEntity
 import de.krisenvorrat.app.data.db.entity.LocationEntity
 import de.krisenvorrat.app.data.db.entity.SettingsEntity
 import de.krisenvorrat.app.domain.repository.ImportExportRepository
+import de.krisenvorrat.shared.model.CategoryDto
+import de.krisenvorrat.shared.model.InventoryDto
+import de.krisenvorrat.shared.model.ItemDto
+import de.krisenvorrat.shared.model.LocationDto
+import de.krisenvorrat.shared.model.SettingDto
 import kotlinx.coroutines.Dispatchers
 import kotlinx.coroutines.flow.first
 import kotlinx.coroutines.withContext
@@ -37,11 +42,11 @@ internal class ImportExportRepositoryImpl @Inject constructor(
         val items = itemDao.getAll().first()
         val settings = settingsDao.getAll().first()
 
-        val exportData = ExportData(
+        val exportData = InventoryDto(
-            categories = categories.map { CategoryExport(id = it.id, name = it.name) },
+            categories = categories.map { CategoryDto(id = it.id, name = it.name) },
-            locations = locations.map { LocationExport(id = it.id, name = it.name) },
+            locations = locations.map { LocationDto(id = it.id, name = it.name) },
             items = items.map { item ->
-                ItemExport(
+                ItemDto(
                     id = item.id,
                     name = item.name,
                     categoryId = item.categoryId,
@@ -56,14 +61,14 @@ internal class ImportExportRepositoryImpl @Inject constructor(
                     lastUpdated = item.lastUpdated
                 )
             },
-            settings = settings.map { SettingExport(key = it.key, value = it.value) }
+            settings = settings.map { SettingDto(key = it.key, value = it.value) }
         )
-        jsonSerializer.encodeToString(ExportData.serializer(), exportData)
+        jsonSerializer.encodeToString(InventoryDto.serializer(), exportData)
     }
 
     override suspend fun importFromJson(json: String): Result<Unit> = withContext(Dispatchers.IO) {
         runCatching {
-            val exportData = jsonSerializer.decodeFromString<ExportData>(json)
+            val exportData = jsonSerializer.decodeFromString<InventoryDto>(json)
             check(exportData.version == 1) { "Unsupported export format version: ${exportData.version}" }
             transaction.execute {
                 categoryDao.upsertAll(exportData.categories.map { CategoryEntity(id = it.id, name = it.name) })

build.gradle.kts

@@ -1,6 +1,7 @@
 // Top-level build file where you can add configuration options common to all sub-projects/modules.
 plugins {
     alias(libs.plugins.android.application) apply false
+    alias(libs.plugins.kotlin.jvm) apply false
     alias(libs.plugins.kotlin.android) apply false
     alias(libs.plugins.kotlin.compose) apply false
     alias(libs.plugins.kotlin.serialization) apply false

gradle/libs.versions.toml

@@ -48,6 +48,7 @@ mockk = { group = "io.mockk", name = "mockk", version.ref = "mockk" }
 
 [plugins]
 android-application = { id = "com.android.application", version.ref = "agp" }
+kotlin-jvm = { id = "org.jetbrains.kotlin.jvm", version.ref = "kotlin" }
 kotlin-android = { id = "org.jetbrains.kotlin.android", version.ref = "kotlin" }
 kotlin-compose = { id = "org.jetbrains.kotlin.plugin.compose", version.ref = "kotlin" }
 kotlin-serialization = { id = "org.jetbrains.kotlin.plugin.serialization", version.ref = "kotlin" }

settings.gradle.kts

@@ -21,3 +21,4 @@ dependencyResolutionManagement {
 
 rootProject.name = "krisenvorrat"
 include(":app")
+include(":shared")

shared/build.gradle.kts

@@ -0,0 +1,21 @@
+plugins {
+    alias(libs.plugins.kotlin.jvm)
+    alias(libs.plugins.kotlin.serialization)
+}
+
+java {
+    sourceCompatibility = JavaVersion.VERSION_11
+    targetCompatibility = JavaVersion.VERSION_11
+}
+
+kotlin {
+    compilerOptions {
+        jvmTarget.set(org.jetbrains.kotlin.gradle.dsl.JvmTarget.JVM_11)
+    }
+}
+
+dependencies {
+    implementation(libs.kotlinx.serialization.json)
+
+    testImplementation(libs.junit)
+}

shared/src/main/kotlin/de/krisenvorrat/shared/model/CategoryDto.kt

@@ -0,0 +1,9 @@
+package de.krisenvorrat.shared.model
+
+import kotlinx.serialization.Serializable
+
+@Serializable
+data class CategoryDto(
+    val id: Int,
+    val name: String
+)

shared/src/main/kotlin/de/krisenvorrat/shared/model/InventoryDto.kt

@@ -0,0 +1,15 @@
+package de.krisenvorrat.shared.model
+
+import kotlinx.serialization.EncodeDefault
+import kotlinx.serialization.ExperimentalSerializationApi
+import kotlinx.serialization.Serializable
+
+@OptIn(ExperimentalSerializationApi::class)
+@Serializable
+data class InventoryDto(
+    @EncodeDefault(EncodeDefault.Mode.ALWAYS) val version: Int = 1,
+    val categories: List<CategoryDto>,
+    val locations: List<LocationDto>,
+    val items: List<ItemDto>,
+    val settings: List<SettingDto>
+)

shared/src/main/kotlin/de/krisenvorrat/shared/model/ItemDto.kt

@@ -0,0 +1,19 @@
+package de.krisenvorrat.shared.model
+
+import kotlinx.serialization.Serializable
+
+@Serializable
+data class ItemDto(
+    val id: String,
+    val name: String,
+    val categoryId: Int,
+    val quantity: Double,
+    val unit: String,
+    val unitPrice: Double,
+    val kcalPer100g: Int?,
+    val expiryDate: String?,
+    val locationId: Int,
+    val minStock: Double,
+    val notes: String,
+    val lastUpdated: Long
+)

shared/src/main/kotlin/de/krisenvorrat/shared/model/LocationDto.kt

@@ -0,0 +1,9 @@
+package de.krisenvorrat.shared.model
+
+import kotlinx.serialization.Serializable
+
+@Serializable
+data class LocationDto(
+    val id: Int,
+    val name: String
+)

shared/src/main/kotlin/de/krisenvorrat/shared/model/SettingDto.kt

@@ -0,0 +1,9 @@
+package de.krisenvorrat.shared.model
+
+import kotlinx.serialization.Serializable
+
+@Serializable
+data class SettingDto(
+    val key: String,
+    val value: String
+)