Add workspace mcp docs

[DidierRLopes]

Adds a new top-level Agents docs section for OpenBB Workspace MCP.

Changes

• Added new Workspace MCP docs pages:
  • /agents/workspace-mcp-overview
  • /agents/workspace-mcp-quickstart
  • /agents/workspace-mcp-tools
• Added Workspace MCP to the sidebar under a new Agents section.
• Documented:
  • Workspace MCP architecture and trust model
  • Sidecar setup
  • Workspace Companion connection flow
  • Codex and Claude Code MCP configuration
  • Workspace MCP tool reference
  • Common workflows for reading Workspace data and adding widgets
• Embedded the Codex demo video.
• Added CMS screenshots for:
  • Running sidecar
  • Workspace MCP Companion menu
  • Connected Workspace MCP Companion
  • Reading Workspace data from Codex
  • Adding a widget from Codex
• Added Agents entries to the local search index.
• Added Agents llms.txt / llms-full.txt output.
• Updated sidebar filtering so /agents/... pages show the expected Workspace docs sections.