feat(01-05): add HOCON config, Flyway migration dir, fail-loud Database.migrate

- application.conf: HOCON with ktor.deployment.port (8080 + ${?PORT}) and
  database.url/user/password (localhost defaults + ${?DATABASE_URL/USER/PASSWORD})
- db/migration/.gitkeep: placeholder so classpath:db/migration resolves
- Database.kt: object Database.migrate(app) reads HOCON config, runs Flyway
  with baselineOnMigrate + validateOnMigrate + cleanDisabled, throws
  IllegalStateException on any failure (D-16 fail-loud contract)
- SLF4J (not Kermit); server logs url+user only, never password

server/src/main/kotlin/dev/ulfrx/recipe/Database.kt

@@ -0,0 +1,31 @@
+package dev.ulfrx.recipe
+
+import io.ktor.server.application.Application
+import org.flywaydb.core.Flyway
+import org.slf4j.LoggerFactory
+
+object Database {
+    private val log = LoggerFactory.getLogger(Database::class.java)
+
+    fun migrate(app: Application) {
+        val url = app.environment.config.property("database.url").getString()
+        val user = app.environment.config.property("database.user").getString()
+        val password = app.environment.config.property("database.password").getString()
+
+        log.info("Connecting to {} as {} and running Flyway migrations", url, user)
+
+        runCatching {
+            Flyway.configure()
+                .dataSource(url, user, password)
+                .locations("classpath:db/migration")
+                .baselineOnMigrate(true)
+                .validateOnMigrate(true)
+                .cleanDisabled(true)
+                .load()
+                .migrate()
+        }.onFailure { ex ->
+            log.error("Flyway migration failed — cannot start server", ex)
+            throw IllegalStateException("Database unreachable or migration failed", ex)
+        }
+    }
+}

server/src/main/resources/application.conf

@@ -0,0 +1,18 @@
+ktor {
+    deployment {
+        port = 8080
+        port = ${?PORT}
+    }
+    application {
+        modules = [ dev.ulfrx.recipe.ApplicationKt.module ]
+    }
+}
+
+database {
+    url = "jdbc:postgresql://localhost:5432/recipe"
+    url = ${?DATABASE_URL}
+    user = "recipe"
+    user = ${?DATABASE_USER}
+    password = "recipe"
+    password = ${?DATABASE_PASSWORD}
+}