chore(docker): add .dockerignore excluding bin/obj/node_modules/wwwroot

.dockerignore

@@ -0,0 +1,41 @@
+# .NET
+**/bin/
+**/obj/
+**/*.user
+
+# Frontend
+frontend/node_modules/
+frontend/dist/
+frontend/.vite/
+frontend/playwright-report/
+frontend/test-results/
+frontend/.pw-data/
+
+# Data / smoke dirs
+_smoke/
+data/
+
+# Editor / VCS
+.git/
+.gitignore
+.vs/
+.idea/
+.vscode/
+
+# Never let host secrets leak in
+.env
+.env.local
+deploy.json
+appsettings.Development.json
+appsettings.Local.json
+
+# The wwwroot in the repo is a placeholder (.gitkeep) — the frontend build
+# stage produces the real one. Don't copy the empty one over the fresh build.
+src/VolcanicCore.Api/wwwroot/
+
+# Docs and repo-only files
+docs/
+README.md
+Dockerfile
+docker-compose.yml
+.dockerignore