docs(acp): update VS Code setup instructions for ACP Client integration

[formulahendry]

What does this PR do?

Updates the ACP documentation for VS Code to match the current ACP Client extension behavior.

The previous instructions told users to point VS Code at acp_registry/, which is not the right setup for the ACP Client extension now that Hermes Agent is available as a built-in pre-configured agent. This change updates the VS Code section to document the current connection flow and keeps a short manual acp.agents fallback for users who want to define Hermes explicitly.

Type of Change

• 📝 Documentation update

Changes Made

• Updated the VS Code setup steps in website/docs/user-guide/features/acp.md
• Removed the outdated instruction to configure VS Code with acp_registry/
• Documented the current ACP Client flow: install the extension, select Hermes Agent, and connect
• Added a manual VS Code settings example using acp.agents with hermes acp

How to Test

1. Open the ACP docs page source at website/docs/user-guide/features/acp.md
2. Confirm the VS Code section tells users to install ACP Client, select Hermes Agent, and connect
3. Confirm the section no longer instructs users to point VS Code at acp_registry/, and that the manual fallback uses acp.agents