docs: scaffold polisher-control foundation

CONTRIBUTING.md

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+# Contributing
+
+## Working style
+
+- Keep changes small and reviewable.
+- Add or update docs when changing protocol, telemetry, state machine, safety, or data layout.
+- Add tests for host-side state-machine and contract behavior before relying on hardware.
+- Never hide clipping, rejected commands, or safety changes; emit explicit events/NACKs.
+
+## Definition of done for a feature
+
+- Implementation exists.
+- Test or bench verification exists.
+- Relevant docs are updated.
+- Safety or contract impact is stated.
+- Antoine-facing open questions are listed if the decision is not locked.