feat(server): add Ktor server module with health endpoint

New Gradle module :server (Kotlin/JVM) with Ktor 3.1.2 framework,
configured as an embedded Netty HTTP server.

server/src/main/kotlin/de/krisenvorrat/server/:
- Application.kt: entry point using EngineMain for HOCON config
- plugins/Routing.kt: GET /health endpoint returning 200 OK
- plugins/Serialization.kt: ContentNegotiation with kotlinx.json

Configuration:
- application.conf (HOCON): host 0.0.0.0, port 8080, module reference
- logback.xml: SLF4J/Logback console logging

Build config:
- server/build.gradle.kts: Ktor plugin with Fat JAR (server.jar)
- libs.versions.toml: Ktor 3.1.2, Logback 1.5.18 dependencies
- settings.gradle.kts: include(:server)
- :server depends on :shared for common DTO models

Tests: 2 tests (health endpoint, 404 on unknown route) via
Ktor testApplication.

Closes #40

build.gradle.kts

@@ -7,4 +7,5 @@ plugins {
     alias(libs.plugins.kotlin.serialization) apply false
     alias(libs.plugins.hilt.android) apply false
     alias(libs.plugins.ksp) apply false
+    alias(libs.plugins.ktor) apply false
 }

gradle/libs.versions.toml

@@ -16,6 +16,8 @@ navigationCompose = "2.8.5"
 kotlinxSerialization = "1.7.3"
 kotlinxCoroutines = "1.9.0"
 mockk = "1.13.13"
+ktor = "3.1.2"
+logback = "1.5.18"
 
 [libraries]
 androidx-core-ktx = { group = "androidx.core", name = "core-ktx", version.ref = "coreKtx" }
@@ -45,6 +47,13 @@ kotlinx-serialization-json = { group = "org.jetbrains.kotlinx", name = "kotlinx-
 androidx-room-testing = { group = "androidx.room", name = "room-testing", version.ref = "room" }
 kotlinx-coroutines-test = { group = "org.jetbrains.kotlinx", name = "kotlinx-coroutines-test", version.ref = "kotlinxCoroutines" }
 mockk = { group = "io.mockk", name = "mockk", version.ref = "mockk" }
+ktor-server-core = { group = "io.ktor", name = "ktor-server-core", version.ref = "ktor" }
+ktor-server-netty = { group = "io.ktor", name = "ktor-server-netty", version.ref = "ktor" }
+ktor-server-content-negotiation = { group = "io.ktor", name = "ktor-server-content-negotiation", version.ref = "ktor" }
+ktor-serialization-kotlinx-json = { group = "io.ktor", name = "ktor-serialization-kotlinx-json", version.ref = "ktor" }
+ktor-server-config-yaml = { group = "io.ktor", name = "ktor-server-config-yaml", version.ref = "ktor" }
+ktor-server-test-host = { group = "io.ktor", name = "ktor-server-test-host", version.ref = "ktor" }
+logback-classic = { group = "ch.qos.logback", name = "logback-classic", version.ref = "logback" }
 
 [plugins]
 android-application = { id = "com.android.application", version.ref = "agp" }
@@ -54,3 +63,4 @@ kotlin-compose = { id = "org.jetbrains.kotlin.plugin.compose", version.ref = "ko
 kotlin-serialization = { id = "org.jetbrains.kotlin.plugin.serialization", version.ref = "kotlin" }
 hilt-android = { id = "com.google.dagger.hilt.android", version.ref = "hilt" }
 ksp = { id = "com.google.devtools.ksp", version.ref = "ksp" }
+ktor = { id = "io.ktor.plugin", version.ref = "ktor" }

server/build.gradle.kts

@@ -0,0 +1,40 @@
+plugins {
+    alias(libs.plugins.kotlin.jvm)
+    alias(libs.plugins.kotlin.serialization)
+    alias(libs.plugins.ktor)
+}
+
+application {
+    mainClass.set("de.krisenvorrat.server.ApplicationKt")
+}
+
+ktor {
+    fatJar {
+        archiveFileName.set("server.jar")
+    }
+}
+
+java {
+    sourceCompatibility = JavaVersion.VERSION_11
+    targetCompatibility = JavaVersion.VERSION_11
+}
+
+kotlin {
+    compilerOptions {
+        jvmTarget.set(org.jetbrains.kotlin.gradle.dsl.JvmTarget.JVM_11)
+    }
+}
+
+dependencies {
+    implementation(project(":shared"))
+
+    implementation(libs.ktor.server.core)
+    implementation(libs.ktor.server.netty)
+    implementation(libs.ktor.server.content.negotiation)
+    implementation(libs.ktor.serialization.kotlinx.json)
+    implementation(libs.logback.classic)
+
+    testImplementation(libs.ktor.server.test.host)
+    testImplementation(libs.junit)
+    testImplementation(libs.kotlinx.serialization.json)
+}

server/src/main/kotlin/de/krisenvorrat/server/Application.kt

@@ -0,0 +1,15 @@
+package de.krisenvorrat.server
+
+import de.krisenvorrat.server.plugins.configureRouting
+import de.krisenvorrat.server.plugins.configureSerialization
+import io.ktor.server.application.*
+import io.ktor.server.netty.*
+
+fun main(args: Array<String>) {
+    EngineMain.main(args)
+}
+
+internal fun Application.module() {
+    configureSerialization()
+    configureRouting()
+}

server/src/main/kotlin/de/krisenvorrat/server/plugins/Routing.kt

@@ -0,0 +1,14 @@
+package de.krisenvorrat.server.plugins
+
+import io.ktor.http.*
+import io.ktor.server.application.*
+import io.ktor.server.response.*
+import io.ktor.server.routing.*
+
+internal fun Application.configureRouting() {
+    routing {
+        get("/health") {
+            call.respondText("OK", ContentType.Text.Plain, HttpStatusCode.OK)
+        }
+    }
+}

server/src/main/kotlin/de/krisenvorrat/server/plugins/Serialization.kt

@@ -0,0 +1,16 @@
+package de.krisenvorrat.server.plugins
+
+import io.ktor.serialization.kotlinx.json.*
+import io.ktor.server.application.*
+import io.ktor.server.plugins.contentnegotiation.*
+import kotlinx.serialization.json.Json
+
+internal fun Application.configureSerialization() {
+    install(ContentNegotiation) {
+        json(Json {
+            prettyPrint = true
+            isLenient = false
+            ignoreUnknownKeys = true
+        })
+    }
+}

server/src/main/resources/application.conf

@@ -0,0 +1,9 @@
+ktor {
+    deployment {
+        port = 8080
+        host = "0.0.0.0"
+    }
+    application {
+        modules = [ de.krisenvorrat.server.ApplicationKt.module ]
+    }
+}

server/src/main/resources/logback.xml

@@ -0,0 +1,13 @@
+<configuration>
+    <appender name="STDOUT" class="ch.qos.logback.core.ConsoleAppender">
+        <encoder>
+            <pattern>%d{yyyy-MM-dd HH:mm:ss.SSS} [%thread] %-5level %logger{36} - %msg%n</pattern>
+        </encoder>
+    </appender>
+
+    <root level="INFO">
+        <appender-ref ref="STDOUT"/>
+    </root>
+
+    <logger name="io.ktor" level="INFO"/>
+</configuration>

server/src/test/kotlin/de/krisenvorrat/server/ApplicationTest.kt

@@ -0,0 +1,38 @@
+package de.krisenvorrat.server
+
+import io.ktor.client.request.*
+import io.ktor.client.statement.*
+import io.ktor.http.*
+import io.ktor.server.testing.*
+import org.junit.Assert.assertEquals
+import org.junit.Test
+
+class ApplicationTest {
+
+    @Test
+    fun test_healthEndpoint_returnsOk() = testApplication {
+        application {
+            module()
+        }
+
+        // When
+        val response = client.get("/health")
+
+        // Then
+        assertEquals(HttpStatusCode.OK, response.status)
+        assertEquals("OK", response.bodyAsText())
+    }
+
+    @Test
+    fun test_unknownRoute_returns404() = testApplication {
+        application {
+            module()
+        }
+
+        // When
+        val response = client.get("/nonexistent")
+
+        // Then
+        assertEquals(HttpStatusCode.NotFound, response.status)
+    }
+}

settings.gradle.kts

@@ -22,3 +22,4 @@ dependencyResolutionManagement {
 rootProject.name = "krisenvorrat"
 include(":app")
 include(":shared")
+include(":server")