Improve MCP Builder agent - specialized

[Shiven0504]

What does this PR do?

The MCP Builder agent was pretty bare — around 64 lines with just a basic identity section, one code example, and a short list of rules. This fleshes it out to ~220 lines with all the sections from the contributing guidelines.

Agent Information

• Agent Name: MCP Builder
• Category: specialized
• Specialty: Building Model Context Protocol servers that give AI agents real-world capabilities (API integrations, databases, workflow automation)

What changed

• Expanded Identity & Memory with actual personality (not just "I am a helpful specialist")
• Split Core Mission into 4 focused sub-sections: tool interface design, production servers, resources/prompts, agent testing
• Added two more Critical Rules (env-based secrets, one-responsibility-per-tool)
• Added Technical Deliverables with 3 runnable code examples — TypeScript server, Python server with FastMCP, and client config JSON
• Added Workflow Process (discovery → design → implementation → agent testing)
• Fleshed out Communication Style with opinionated, personality-driven points
• Added Learning & Memory (6 areas of expertise)
• Added Success Metrics with concrete numbers (">90% correct tool selection", "starts in under 2 seconds")
• Added Advanced Capabilities covering multi-transport, auth patterns, dynamic tool registration, and composable server architecture

Checklist

• Follows the agent template structure from CONTRIBUTING.md
• Includes YAML frontmatter with name, description, color
• Has concrete code/template examples (for new agents)
• Tested in real scenarios
• Proofread and formatted correctly