Polymarket activity endpoint should allow empty query params

[DenisCarriere]

Summary

GET /v1/polymarket/markets/activity currently rejects requests that do not include user, token_id, or condition_id.

Current error:

{
  "status": 400,
  "code": "bad_query_input",
  "message": "Provide at least one of user, token_id, or condition_id"
}

This endpoint should allow empty query params and return activity without requiring a filter.

Acceptance criteria

• Requests to /v1/polymarket/markets/activity with no filter params return a successful response.
• Existing optional filters continue to work when provided.
• Query validation no longer requires at least one of user, token_id, or condition_id.
• Add or update tests/docs as appropriate.