Move Docker-related files to contrib/stella directory and update paths accordingly

contrib/stella/.dockerignore

@@ -0,0 +1,20 @@
+# Exclude heavy or host-specific data from Docker build context
+# Fixes: failed to solve: error from sender: open cmd/benchmark/data/postgres: permission denied
+
+# Benchmark data and reports (mounted at runtime via volumes)
+../../cmd/benchmark/data/
+cmd/benchmark/reports/
+
+# VCS and OS cruft
+.git
+.gitignore
+**/.DS_Store
+**/Thumbs.db
+
+# Go build cache and binaries
+**/bin/
+**/build/
+**/*.out
+
+# Allow web dist directory (needed for embedding)
+!app/web/dist/