* feat: make session_name nullable for documents and update related SDKs
- Introduced a migration to make the `session_name` column in the documents table nullable, allowing for sessionless dreams.
- Updated Python and TypeScript SDKs to reflect the optional nature of `session_id` in conclusion creation and related methods.
- Enhanced tests to cover scenarios for creating conclusions without a session ID, ensuring proper handling of sessionless conclusions.
- Adjusted documentation and type definitions to clarify the optional session context in various components.
* chore: add migration test
* fix: ensure orphaned sessions exist during downgrade for nullable session_name migration
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