Update .gitignore to include .env and .DS_Store files

Add .cursor autodevelopment system

.cursor/rules/docker.mdc

@@ -0,0 +1,15 @@
+---
+description: "Docker and Docker Compose conventions: multi-stage builds, security, image pinning, health checks"
+globs: ["**/Dockerfile*", "**/docker-compose*", "**/.dockerignore"]
+---
+# Docker
+
+- Use multi-stage builds to minimize image size
+- Pin base image versions (never use `:latest` in production)
+- Use `.dockerignore` to exclude build artifacts, `.git`, `node_modules`, etc.
+- Run as non-root user in production containers
+- Use `COPY` over `ADD`; order layers from least to most frequently changed
+- Use health checks in docker-compose and Dockerfiles
+- Use named volumes for persistent data; never store state in container filesystem
+- Centralize environment configuration; use `.env` files only for local dev
+- Keep services focused: one process per container