docs: write score API reference — GET /api/score/:userId

[basanth-p]

Summary

Write the full API reference page for the GET /api/score/:userId endpoint.

Content to cover

1. Endpoint overview — what it returns, when to use
2. Authentication — Bearer token, how to obtain
3. Path parameters — userId
4. Response schema — score, bucket, breakdown[], computed_at
5. Score buckets — Beginner / Active / Expert / Elite ranges
6. Error responses — 401, 404, 429, 500
7. Code examples — cURL, JavaScript fetch, Python requests

Deliverable

/api-reference/score.mdx

Depends on

• core score API scaffold (patchid/core#10)
• Docs site scaffold (chore: scaffold docs site — structure, getting started, API reference baseline #1)