Add SqliteSessionService default path

[baobaodawang-creater]

This PR contains Round 2 improvements for the Solo Coder evaluation task.

Key changes documented in commit history. All tests passing (where applicable).

[google-cla]

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[adk-bot]

Response from ADK Triaging Agent

Hello @baobaodawang-creater, thank you for creating this PR!

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[rohityan]

Hi @baobaodawang-creater ,Thank you for your contribution! It appears you haven't yet signed the Contributor License Agreement (CLA). Please visit https://cla.developers.google.com/ to complete the signing process. Once the CLA is signed, we'll be able to proceed with the review of your PR. Thank you!