chore: add docker deployment support

docs/superpowers/specs/2026-05-13-docker-configuration-design.md

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+# Docker Configuration Design
+
+## Goal
+
+Add Docker support for both production deployment and local development of the Vite React app, while making the default production path minimize Docker downloads.
+
+## Architecture
+
+Production builds the static app on the host using the already-installed npm dependencies, then uses a single-stage `nginx:stable-alpine3.23-slim` Dockerfile to copy and serve `dist` on port `80`. This avoids downloading a Node image and reinstalling npm packages during the Docker deployment.
+
+Development remains an optional separate Dockerfile and compose file. It installs dependencies, runs `npm run dev`, exposes Vite on port `3000`, and mounts source files from the host while keeping `node_modules` inside the container. It is not the low-download production path.
+
+## Files
+
+- `.dockerignore` excludes dependencies, unrelated build output, logs, and local env files from Docker build context, while retaining `dist` for the production image.
+- `Dockerfile` creates a small production image from the host-built static output.
+- `nginx.conf` serves static assets and falls back to `index.html` for React Router routes.
+- `docker-compose.yml` runs the production image on host port `8080`.
+- `Dockerfile.dev` runs the Vite dev server.
+- `docker-compose.dev.yml` runs the development container on host port `3000`.
+- `README.md` documents the Docker commands.
+
+## Environment
+
+The current Vite config injects `GEMINI_API_KEY` during build. Production therefore reads `.env.local` during the host-side `npm run build` command and copies the resulting static bundle into the container. Development reads environment values from `.env.local` when present.
+
+## Verification
+
+- Run `npm run lint`.
+- Run `npm run build`.
+- Build the production Docker image after a host-side `npm run build`.
+- Optionally run the compose services if Docker is available.