Add MCP development plan and Axis2 modernization roadmap

- MCP.md: Full MCP implementation plan capturing current development
  state — Track A (OpenAPI-driven bridge: A1 /openapi-mcp.json endpoint,
  A2 stdio bridge JAR, A3 team validation, A4 HTTP/SSE) and Track B
  (native axis2-transport-mcp, stdio first then HTTP/SSE). Includes
  design decisions, build dependencies, and immediate next actions.
- AXIS2_MODERNIZATION_PLAN.md: 7-phase modernization plan (Spring Boot
  starter, OpenAPI annotation bridge, REST dual-protocol, MCP bridge,
  HTTP/2 publication, native MCP transport, community positioning)

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

Author: robertlazarski