fix: Update jac-mcp-chatbot backend with the latest jaseci stack

[Hirudika4]

• Changed the text parameter in both ImageChat.chat and VideoChat.chat to explicitly use the Text type, ensuring message content is consistently typed throughout the codebase.
• Updated walker and router initialization and routing logic to use Root entry and the ?: syntax for more robust and explicit node selection.
• Modified the instantiation of the llm global to pass the verbose flag via the config dictionary.
• Updated the import for the Document class to use langchain_core.documents instead of langchain.schema.document, aligning with the latest library structure.
• Fixed the command in the README.md to use jac start instead of the outdated jac serve.

[Copilot]

Pull request overview

This pull request updates the jac-mcp-chatbot backend to align with the latest jaseci stack conventions, including modernizing Jac syntax, updating library imports, and fixing documentation. The PR addresses syntax deprecations and ensures consistency with the current Jac language specification.

Changes:

• Updated Jac walker syntax from legacy backtick notation to modern Root entry and (?:Type) node filter syntax
• Migrated langchain Document import from deprecated langchain.schema.document to langchain_core.documents
• Wrapped text parameters with explicit Text() type constructors for type consistency in Image/VideoChat methods
• Updated README command from deprecated jac serve to jac start

Reviewed changes

Copilot reviewed 4 out of 4 changed files in this pull request and generated 1 comment.

File	Description
tools.jac	Updates Document import to use langchain_core.documents instead of deprecated langchain.schema.document
server.jac	Modernizes walker syntax to use Root entry and (?:Type) filters; modifies LLM configuration (has issue with verbose parameter placement)
server.impl.jac	Wraps visitor.message with Text() constructor for type-safe parameter passing to respond_with_image/video methods
README.md	Updates command from deprecated jac serve to current jac start

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[Copilot]

The verbose parameter should be a top-level parameter of the Model constructor, not inside the config dictionary. According to the byllm documentation and conventions used throughout the codebase (e.g., task_manager/byllm/BE/v1/main.jac:8), the config dictionary is reserved for advanced settings like api_base, http_client, and ca_bundle. The correct syntax should be: Model(model_name='gpt-4o-mini', verbose=False)

Suggested change

	glob llm = Model(model_name='gpt-4o-mini',config={"verbose": False});
	glob llm = Model(model_name='gpt-4o-mini', verbose=False);