feat: add Unity assets, frontend, update gitignore - remove dev artifacts

.gitignore

@@ -15,6 +15,21 @@ game/[Aa]ssets/[Ss]treamingAssets/aa/
 rolld_backend/game/node_modules/
 rolld_backend/game/.env
 
+# Frontend build output & dependencies
+frontend/node_modules/
+frontend/dist/
+
+# WebGL build artifacts (generated by Unity)
+build/
+nouveau_build/
+
+# Dev-only tools (buildgate was used for manual dev deploys, remplacé par Coolify)
+rolld_buildgate/
+
+# Sensitive files
+git_key
+check_wasm.js
+
 # OS
 .DS_Store
 Thumbs.db