Adds the public telemetry data contract README, links it from contributor docs, and adds a focused README contract test for generated helper names.
Verification:
- git diff --check origin/master..HEAD
- pnpm exec vitest run packages/shared/src/telemetry/readme-contract.test.ts
- PR CI green
- Greptile 5/5
Co-Authored-By: Paperclip <noreply@paperclip.ing>
Nicky Leach