[appkit plugin] [5/x] Add chat server plugin to @databricks/appkit-agent #561

Job	Run time
format	11s
typechecking for integrations/openai	13s
typechecking for integrations/dspy	12s
ruff check for integrations/openai	10s
ruff check for integrations/llamaindex	10s
typechecking for databricks_mcp	11s
ruff check for integrations/dspy	12s
typechecking for integrations/langchain	12s
ruff check for databricks_mcp	10s
ruff check for .	13s
typechecking for .	13s
ruff check for integrations/langchain	10s
typechecking for integrations/llamaindex	12s
	2m 29s

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