[WIP] Add spec validation with user feedback for config.edn

[Copilot]

• Add expound dependency for friendly error messages
• Create clojure-mcp.config.spec namespace with configuration validation specs
• Define basic type specs (::path, ::env-ref, etc.)
• Define specs for all configuration keys based on existing get-* functions
• Define complex nested specs for resources, prompts, models, and agents
• Create validation functions with expound integration
• Integrate validation into process-config function (minimal change approach)
• Create comprehensive tests for the validation system
• Verify validation works on example configurations
• Test error handling with friendly expound messages

This implementation will provide immediate feedback on invalid configurations while maintaining minimal changes to existing code. The validation will be integrated directly into process-config to catch errors early.

Fixes #92.

---

💡 You can make Copilot smarter by setting up custom instructions, customizing its development environment and configuring Model Context Protocol (MCP) servers. Learn more Copilot coding agent tips in the docs.

[Copilot]

@bhauman 👋 This repository doesn't have Copilot instructions. With Copilot instructions, I can understand the repository better, work faster and produce higher quality PRs.

I can generate a .github/copilot-instructions.md file for you automatically. Click here to open a pre-filled issue and assign it to me. I'll write the instructions, and then tag you for review.