feat: add runnable :samples module (#47)

* build: scaffold :samples module (issue #37)

* feat: add runnable, verified examples to :samples (issue #37)

* ci,docs: run :samples in CI and document ./gradlew :samples:run (issue #37)

build.gradle.kts

@@ -59,6 +59,11 @@ repositories {
     mavenCentral()
 }
 
+apiValidation {
+    // :samples is a dev-facing examples module, not a published artifact, so it has no .api dump.
+    ignoredProjects.add("samples")
+}
+
 dependencies {
     // Include this module's own docs in the aggregation — DGP v2 requires the
     // aggregating project to list itself explicitly.