docs(architecture): update MCP integration section

[galligan]

Summary

Architecture documentation describes outdated MCP integration approach.

Findings

Issue ID	Description
ARCH-001	docs/architecture/README.md MCP section claims JSON-RPC with 5 methods

Actual Implementation

• Uses rmcp SDK v0.8.1
• Has 2 consolidated tools with action-based dispatch
• Does not use raw JSON-RPC

Files to Update

• docs/architecture/README.md - Update MCP Integration section

Source of Truth

• crates/blz-mcp/src/server.rs
• Cargo.toml for rmcp version

Priority

High - Misleading architecture documentation.

[linear]

BLZ-316