Add Pydantic response models for OpenAPI/Swagger docs

[HaraldeRoessler]

Summary

The Swagger docs at /docs show empty response schemas ({}) for all endpoints because no response_model is set on the FastAPI route decorators. This makes it impossible for plugin/SDK developers to know what fields the API returns.

The problem

All three sources tell a different story:

Endpoint	API returns	Swagger shows	Plugin expects
/identity/verify/{did}	{did, verified, reputation}	{}	{did, verified, message, trustScore}
/skill/trust-score/{did}	{did, trust_score, grade, breakdown, ...}	{}	{did, score, grade, sybilRisk}
/reputation/query/{did}	{did, score, total_ratings}	{}	not used

This caused the moltrust-openclaw plugin to show 'undefined' — fixed in MoltyCel/moltrust-openclaw#1.

Changes

Adds Pydantic response models for 6 core endpoints:

• VerifyResponse for GET /identity/verify/{did}
• ReputationResponse for GET /reputation/query/{did}
• TrustScoreResponse + TrustScoreBreakdown for GET /skill/trust-score/{did}
• DIDDocumentResponse + DIDDocumentMetadata for GET /identity/resolve/{did}
• HealthResponse for GET /health
• RateResponse for POST /reputation/rate

Test plan

• Verify /docs shows populated response schemas
• Verify endpoints still return correct data

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