Add Deep Agents Code local adapter

[sarahwooders]

Summary

• add a fixed-path normalizeDeepAgentsCode wrapper for ~/.deepagents/.state/sessions.db
• require an explicit thread ID and delegate checkpoint loading/replay to the generic official-Python Deep Agents adapter
• retag only normalized metadata to deepagents-code, with matching Python API, docs, and tests

This PR is stacked on #2.

Testing

• DEEPAGENTS_TEST_PYTHON=/tmp/trajectory-deepagents-sdk-local/.venv/bin/python bun run check (47 passed)
• PYTHONPATH=python/src /tmp/trajectory-deepagents-sdk-local/.venv/bin/python -m unittest discover -s python/tests -v (9 passed)
• built package import smoke
• npm pack --dry-run
• git diff --check

[cpacker]

This draft still targets agent/deepagents-sdk-local, even though the base PR merged into main. It is clean only against that obsolete branch; integrating the current head into main conflicts across the public API/types, Python wrapper and generated bundle, tests, and README.

Please retarget/rebase and reconstruct the diff against current main, then rerun the full TypeScript/Python parity and generated-artifact checks before requesting code review. The core approach of delegating to the generic checkpoint adapter and retagging metadata is directionally sound, but reviewing the stale combined diff further would not be reliable.

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