feat(01-01): create Mill build configuration with ZIO dependencies

- Mill 1.1.1 build file with Scala 3.3.4
- ZIO 2.1.14, zio-http 3.0.1, zio-config 4.0.2
- Quill 4.8.5, PostgreSQL driver 42.7.4, Flyway 10.21.0
- Assembly rules for fat JAR with service file merging
- .gitignore for Mill artifacts (out/, mill executable)

build.mill

@@ -0,0 +1,49 @@
+package build
+
+import mill._
+import mill.scalalib._
+import mill.scalalib.Assembly._
+
+object summercms extends ScalaModule {
+  def scalaVersion = "3.3.4"
+
+  def mvnDeps = Seq(
+    // ZIO Core
+    mvn"dev.zio::zio:2.1.14",
+
+    // ZIO HTTP
+    mvn"dev.zio::zio-http:3.0.1",
+
+    // ZIO Config
+    mvn"dev.zio::zio-config:4.0.2",
+    mvn"dev.zio::zio-config-typesafe:4.0.2",
+    mvn"dev.zio::zio-config-magnolia:4.0.2",
+
+    // Database - Quill with ZIO
+    mvn"io.getquill::quill-jdbc-zio:4.8.5",
+
+    // PostgreSQL JDBC Driver
+    mvn"org.postgresql:postgresql:42.7.4",
+
+    // Flyway for migrations
+    mvn"org.flywaydb:flyway-core:10.21.0",
+    mvn"org.flywaydb:flyway-database-postgresql:10.21.0"
+  )
+
+  def scalacOptions = Seq(
+    "-deprecation",
+    "-feature",
+    "-unchecked",
+    "-Xfatal-warnings"
+  )
+
+  // Assembly configuration for fat JAR
+  def assemblyRules = super.assemblyRules ++ Seq(
+    // Merge service files
+    Rule.Append("META-INF/services/.*"),
+    // Exclude signature files
+    Rule.Exclude("META-INF/.*\\.SF"),
+    Rule.Exclude("META-INF/.*\\.DSA"),
+    Rule.Exclude("META-INF/.*\\.RSA")
+  )
+}