docs: add JSON-RPC MCP Integration Guide

New doc at src/site/xdoc/docs/json-rpc-mcp-guide.xml covering:

- /openapi-mcp.json catalog endpoint (schema, HTTP headers, cache-control)
- _meta block: axis2JsonRpcFormat, authHeader, tokenEndpoint
- Per-tool fields: x-axis2-payloadTemplate, x-requiresAuth, MCP 2025 annotations
- Axis2 JSON-RPC envelope format with parsing sequence explanation
- enableJSONOnly mode
- Two-phase Bearer token auth flow (matches pyRapi/rapi-mcp pattern)
- Correlation ID error handling (Bad Request [errorRef=<uuid>])
- Full unit test feature matrix: McpCatalogGeneratorTest (50+ tests),
  McpCatalogHandlerTest (17 tests), McpAxis2PayloadTest (30 tests),
  JSONRPCIntegrationTest (9 tests), pyRapi test_auth.py (18 tests)
- Not-implemented table: empty inputSchema properties, no rich descriptions,
  no Resources/Prompts, conservative annotation defaults, no streaming,
  no batch calls, no semantic query layer, no pagination, SOAP fault format,
  no API key management, moneyball empty, gateway not wired to Axis2
- Comparison table: Axis2 today vs Data API Phase 1 (Q2 2026)
- Python compatibility notes per repo: rapi-mcp, pyRapi,
  internal-alpha-theory-mcp (3 servers), atds_research, hermes_at, moneyball
- Minimal catalog-driven MCP server template

Audience: Python MCP developers targeting AT RAPI services, and developers
who have read DATA_API_VISION.md / DATA_API_INTERFACE_DESIGN.md.

Add as section 23.4 in toc.xml under JSON Support.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

Author: robertlazarski