Use the not-so-new --json arg of curl

[atesgoral]

curl has a --json arg to replace this entire boilerplate:

-X POST -H "Content-Type: application/json"

(Edit: Actually -X POST is already redundant in the presence of -d)

See https://daniel.haxx.se/blog/2022/02/02/curl-dash-dash-json/

Updating examples to use modern curl.

Motivation and Context

1. Reduce verbosity
2. Promote the --json feature

How Has This Been Tested?

Ran one of the modified commands without errors

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)
• Documentation update

Checklist

• I have read the MCP Documentation
• My code follows the repository's style guidelines
• New and existing tests pass locally
• I have added appropriate error handling
• I have added or updated documentation as needed

[koic]

Nice! It refines into a simpler command without losing its intent.