Import documentation: README.md

Import the existing local project snapshot. This commit organizes existing files; it does not represent newly developed functionality.

README.md

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+# CShare
+
+CShare is a production-shaped file sharing app with a Vite/React frontend and a TypeScript/Express backend. It supports file upload, expiring share links, recipient previews for small safe files, downloads, dashboard stats, and an admin API.
+
+## Project Layout
+
+- `cshare-app/` - React frontend, Vite build, precompressed static assets.
+- `backend/` - Express API, local disk storage adapter, JSON metadata store, auth primitives, admin API.
+- `PRODUCTION.md` - deployment notes, required env, Nginx guidance.
+- `deploy/` - sample service and reverse-proxy config.
+
+## Local Development
+
+Backend:
+
+```sh
+cd backend
+npm install
+npm run dev
+```
+
+Frontend:
+
+```sh
+cd cshare-app
+npm install
+VITE_API_BASE_URL=http://localhost:4001 npm run dev
+```
+
+## Final Checks
+
+```sh
+cd backend && npm run check
+cd ../cshare-app && npm run check
+```
+
+Frontend builds create gzip and Brotli assets in `cshare-app/dist/`. Backend production startup requires strong `JWT_ACCESS_SECRET`, `JWT_REFRESH_SECRET`, and `ADMIN_API_KEY` values.
+
+## Publish Notes
+
+Before publishing, configure the environment in `PRODUCTION.md`, serve `cshare-app/dist/` with a static host or Nginx, and proxy `/api` plus `/health` to the backend. The included local JSON/disk persistence is suitable for a single-server launch; move to PostgreSQL/R2 before depending on durable multi-server storage.