Add athlete audit ingestion and history APIs under /api/v1

[Copilot]

This PR implements backend support for daily athlete audit submission and historical retrieval. It introduces a write path for audit metrics with strict input validation and a read path for athlete-specific audit history ordered newest-first.

• API surface

  • Added POST /api/v1/audit to accept athlete daily audit payloads.
  • Added GET /api/v1/athletes/{id}/history to return all stored audit logs for an athlete, sorted by most recent date/time.

• Validation and error semantics

  • Added schema-level validation for:
    • date format (YYYY-MM-DD)
    • non-empty scores
    • score bounds (1..10, inclusive)
  • Normalized invalid payload handling to 400 Bad Request.
  • Returns 404 Not Found when athlete ID does not exist for both endpoints.

• Persistence and retrieval

  • Added audit log storage in backend data layer (audit_logs.json).
  • Centralized created_at generation in persistence helper to keep timestamping consistent.
  • Added robust history parsing that skips malformed persisted rows instead of failing whole responses.

• Docs

  • Updated README API endpoint table with the two new /api/v1 endpoints.

# main.py (new endpoint shape)
@app.post("/api/v1/audit")
async def create_audit_log(req: AuditRequest):
    if not get_athlete(req.athlete_id):
        raise HTTPException(status_code=404, detail=f"Athlete {req.athlete_id} not found")
    audit_entry = add_audit_log({
        "athlete_id": req.athlete_id,
        "date": req.date,
        "scores": req.scores,
    })
    return {"status": "created", "audit": audit_entry}