This commit refactors the Mcp_sdk module to use a direct approach instead of
OCaml functors for creating servers. The changes include:

- Remove the MakeServer functor and Server module
- Create direct functions for working with servers
- Expose register_* and add_* functions for tools, resources, and prompts
- Update the capitalize_sdk.ml example to use the new API
- Simplify the server creation and configuration process

The non-functor API provides a more straightforward approach for creating
MCP servers in OCaml.

🤖 Generated with [Claude Code](https://claude.ai/code)

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