Feat/add parts support to http api

[SeanZ]

Summary

Add support for parts parameter in the HTTP API add_message endpoint, enabling feature parity with the Python SDK.

Previously, the HTTP API only supported content: str, which limited the ability to store structured message parts (TextPart, ContextPart, ToolPart). This PR adds an optional parts parameter while maintaining backward compatibility with the existing content parameter.

Type of Change

• New feature (feat)
• Bug fix (fix)
• Documentation (docs)
• Refactoring (refactor)
• Other

Changes

API Changes

• POST /api/v1/sessions/{session_id}/messages now accepts either:
  • content (string) - simple mode, backward compatible
  • parts (array) - full Part support mode

Files Modified

• openviking/server/routers/sessions.py - Server endpoint
• openviking/client/local.py - Local client
• openviking_cli/client/http.py - HTTP client
• docs/zh/api/05-sessions.md - Chinese documentation
• docs/en/api/05-sessions.md - English documentation

Testing

# Test simple mode (backward compatible)
curl -X POST http://localhost:1933/api/v1/sessions/test/messages \
  -H "Content-Type: application/json" \
  -d '{"role": "user", "content": "Hello"}'

# Test parts mode
curl -X POST http://localhost:1933/api/v1/sessions/test/messages \
  -H "Content-Type: application/json" \
  -d '{"role": "assistant", "parts": [{"type": "text", "text": "Response"}]}'

Checklist

• Code follows project style guidelines
• Documentation updated
• Tests added (TODO: add unit tests)

[CLAassistant]

All committers have signed the CLA.