docs: MCP guide: GitHub links, modelcontextprotocol.io, clarify auth

- Quick Start: replaced file paths with clickable GitHub links for
  both sample READMEs (Tomcat 11 and WildFly)
- What is MCP: linked modelcontextprotocol.io and Wikipedia article
- Two-Phase Bearer Token: clarified that the auth flow is implemented
  by the sample application's Spring Security configuration, not by
  Axis2 itself. Axis2 is a web services framework that does not
  impose any authentication mechanism.

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