fix: Session.add_message() support parts parameter

[qin-ctx]

Description

Fix Session.add_message() and OVClient.add_message() to support the parts parameter (TextPart, ContextPart, ToolPart), aligning the wrapper API with the underlying BaseClient and documentation.

Related Issue

Fixes #397

Type of Change

• Bug fix (non-breaking change that fixes an issue)

Changes Made

• openviking/client/session.py: Updated Session.add_message() signature to accept optional parts: List[Part] in addition to content: str. When parts is provided, converts Part dataclass objects to dicts via dataclasses.asdict() before passing to the underlying client.
• examples/claude-memory-plugin/scripts/ov_memory.py: Updated OVClient.add_message() to expose the parts parameter, passing it through to the underlying sync client.

Testing

• I have performed a self-review of my code
• New and existing unit tests pass locally with my changes

Checklist

• My code follows the project coding style
• I have performed a self-review of my code
• My changes generate no new warnings

Additional Notes

The underlying infrastructure (BaseClient, AsyncHTTPClient, LocalClient, server-side Session) all already support parts. Only the user-facing Session wrapper class and the OVClient example were missing this parameter.

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