[bugfix] fix agent_template test

[Jintao-Huang]

No description provided.

[gemini-code-assist]

Code Review

This pull request refactors the way agent templates are assigned within the framework, moving from direct object assignment to setting a string identifier on the _agent_template attribute. These changes are applied across various example scripts and test files. A review comment points out that a test case was disabled in the __main__ block of tests/test_align/test_template/test_agent.py, which may have been a temporary change for local debugging that should be reverted to maintain full test coverage.

[gemini-code-assist]

In the __main__ block, test_qwen3_5() has been commented out while test_deepseek_v3_1() was enabled. If this change was only intended for local debugging, please revert it or enable both tests to maintain full coverage when running the script directly.