Implement Phase 1 core translation engine (95 tests passing)

Custom i18n module with HOCON translation files, CLDR-aware pluralization
for 40+ locales, namespace::group.item key resolution, :name/:Name/:NAME
parameter interpolation, and locale fallback chains. No effect system deps.

build.sbt

@@ -0,0 +1,20 @@
+lazy val root = (project in file("."))
+  .settings(
+    name         := "summer-phrasebook",
+    organization := "com.golem15.summer",
+    version      := "0.1.0-SNAPSHOT",
+    scalaVersion := "3.3.4",
+
+    libraryDependencies ++= Seq(
+      "com.typesafe" % "config"  % "1.4.3",
+      "org.scalameta" %% "munit" % "1.0.3" % Test,
+    ),
+
+    scalacOptions ++= Seq(
+      "-Wunused:all",
+      "-deprecation",
+      "-feature",
+    ),
+
+    testFrameworks += new TestFramework("munit.Framework"),
+  )