Initial public Omnigraph repository

CONTRIBUTING.md

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+# Contributing
+
+Small bug fixes and documentation improvements are welcome directly through pull
+requests.
+
+For larger changes, please open an issue or design discussion first so the
+proposed direction is clear before implementation starts.
+
+## Development
+
+```bash
+cargo build --workspace
+cargo test --workspace
+```
+
+If you touch S3-backed flows, the CI model uses a local RustFS instance for
+integration tests.
+
+## Pull Requests
+
+- keep changes focused
+- include tests for behavior changes when practical
+- update public docs when the user-facing surface changes