refactor database model for agent management · ValueCell-ai/valuecell@ff974eb

The process '/opt/hostedtoolcache/ruff/0.13.0/x86_64/ruff' failed with exit code 1

python/valuecell/server/db/models/agent.py:8:32: F401 `typing.Optional` imported but unused

python/valuecell/server/db/models/agent.py:8:26: F401 `typing.List` imported but unused

python/valuecell/server/db/models/agent.py:7:22: F401 `datetime.datetime` imported but unused

python/valuecell/server/db/init_db.py:133:24: F401 `os` imported but unused

python/valuecell/server/db/connection.py:3:8: F401 `os` imported but unused

python/valuecell/server/db/__init__.py:9:1: F403 `from .models import *` used; unable to detect undefined names

python/scripts/init_database.py:13:1: E402 Module level import not at top of file

python/scripts/init_database.py:5:8: F401 `os` imported but unused

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