docs: revise agent proposal to match official Mendix docs

Corrects the smart-app examples and MDL syntax after cross-referencing
the official Mendix Agent Editor, Agent Commons, Conversational UI,
MCP Client, and MCP Server documentation.

Key corrections:
- Tools, knowledge bases, and MCP services are attached to the agent
  document itself, not wired up at runtime in the action microflow.
- Added TOOLS (...), KNOWLEDGE BASES (...), MCP SERVICES (...) clauses
  to CREATE AGENT with ACCESS modifiers for user approval.
- Introduces CALL AGENT WITH HISTORY, CALL AGENT WITHOUT HISTORY, and
  NEW CHAT FOR AGENT as new MDL microflow statements mapping to the
  Agents Kit toolbox activities.
- Added prerequisites section (Encryption setup, ASU_AgentEditor as
  after-startup microflow, model key constants).
- Tool microflows take primitive parameters (whose names become the
  tool's JSON schema), not the Request/ToolCall objects.
- MCP Server example now uses MCPServer.CreateMCPServer + AddTool
  instead of a custom Published REST Service.
- Phase 4 expanded to include CREATE MODEL, CREATE KNOWLEDGE BASE,
  and CREATE CONSUMED MCP SERVICE document types.
- Open Questions and Risk Assessment updated for the new scope.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

Author: ako