chore: project scaffolding and CI

Gradle 9.4 multi-module setup with Kotlin DSL and version catalog.
GitHub Actions builds on push and PR with JDK 25 (Temurin).

.gitignore

@@ -0,0 +1,50 @@
+# Claude Code + GSD planning (local only)
+.claude/
+.planning/
+
+# Gradle / Kotlin
+.gradle/
+.kotlin/
+build/
+!gradle/wrapper/gradle-wrapper.jar
+!**/src/**/build/
+gradle-app.setting
+.gradletasknamecache
+
+# Java
+*.class
+hs_err_pid*
+replay_pid*
+
+# IDE
+.idea/
+*.iml
+*.iws
+*.ipr
+out/
+.vscode/
+*.code-workspace
+
+# Eclipse
+.project
+.classpath
+.settings/
+bin/
+
+# OS
+.DS_Store
+Thumbs.db
+desktop.ini
+
+# Local env / secrets
+.env
+.env.local
+*.local
+
+# Logs / dev server artifacts
+*.log
+logs/
+/run/
+/server/
+
+.tools