api: Use Huma to generate swagger docs and parse JSON automatically (#262)

## Motivation and Context

Currently there's a lot of unsafe manual JSON unmarshalling/marshalling,
and we have to manually keep the openapi schema in sync.

This PR migrates the API to
[Huma](https://github.com/danielgtaylor/huma), which appears like a
popular, well-maintained way to build APIs in Golang. I'm not a Golang
expert, but seemed highly recommended by Reddit + Claude and has a
decent star count. It provides automatic openapi spec generation and
docs hosting, JSON parsing, as well as the ability to add auth
middlewares etc.

## How Has This Been Tested?

Running locally, and poking at the endpoints

## Breaking Changes

Docs are served at `/docs` rather than `/v0/swagger/index.html` now

## Types of changes
<!-- What types of changes does your code introduce? Put an `x` in all
the boxes that apply: -->
- [ ] Bug fix (non-breaking change which fixes an issue)
- [x] New feature (non-breaking change which adds functionality)
- [x] Breaking change (fix or feature that would cause existing
functionality to change)
- [x] Documentation update

## Checklist
<!-- Go over all the following points, and put an `x` in all the boxes
that apply. -->
- [x] I have read the [MCP
Documentation](https://modelcontextprotocol.io)
- [x] My code follows the repository's style guidelines
- [x] New and existing tests pass locally
- [x] I have added appropriate error handling
- [x] I have added or updated documentation as needed

## Additional context
<!-- Add any other context, implementation notes, or design decisions
-->

internal/api/handlers/v0/response.go

@@ -0,0 +1,23 @@
+package v0
+
+// Response is a generic wrapper for Huma responses
+// Usage: Response[HealthBody] instead of HealthOutput
+type Response[T any] struct {
+	Body T
+}
+
+// Example usage:
+// Instead of:
+//   type HealthOutput struct {
+//       Body HealthBody
+//   }
+//
+// You could use:
+//   type HealthOutput = Response[HealthBody]
+//
+// Or directly in the handler:
+//   func(...) (*Response[HealthBody], error) {
+//       return &Response[HealthBody]{
+//           Body: HealthBody{...},
+//       }, nil
+//   }