Initial service implementation

CONTRIBUTING.md

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+# Contributing
+
+## Setup
+
+1. Copy `.env.example` to `.env`.
+2. Install dependencies with `npm install`.
+3. Start the app with `npm run dev` or `docker compose up --build`.
+
+## Before opening changes
+
+Run:
+
+```bash
+npm run build
+npm test
+```
+
+If you are touching the running service flow, also run:
+
+```bash
+npm run smoke
+```
+
+## Notes
+
+- Keep the code modular. Avoid adding unrelated logic into a single file.
+- Preserve the cleanup guarantees around temporary clone directories.
+- Do not commit private SSH keys.