fix(session): allow explicit role_id passthrough

[qin-ctx]

Description

Allow session add-message requests to persist explicit role_id values without server-side caller-role or format enforcement.

Related Issue

Type of Change

• Bug fix (non-breaking change that fixes an issue)
• New feature (non-breaking change that adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• Documentation update
• Refactoring (no functional changes)
• Performance improvement
• Test update

Changes Made

• Remove the USER-specific rejection path for explicit session message role_id values.
• Stop normalizing or validating role_id format on the sessions add-message route and only auto-fill when the field is missing or empty.
• Update the server session API tests to cover explicit role_id passthrough for USER requests, including raw sender-style identifiers.

Testing

• I have added tests that prove my fix is effective or that my feature works
• New and existing unit tests pass locally with my changes
• I have tested this on the following platforms:
  • Linux
  • macOS
  • Windows

Local verification:

• python -m pytest -o addopts='' tests/server/test_api_sessions.py
• python -m compileall openviking/server/routers/sessions.py tests/server/test_api_sessions.py

Checklist

• My code follows the project's coding style
• I have performed a self-review of my code
• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation
• My changes generate no new warnings
• Any dependent changes have been merged and published

Screenshots (if applicable)

Additional Notes

Existing test output includes pre-existing Pydantic deprecation warnings unrelated to this change.

[github-actions]

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[github-actions]

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