Add embedded CLI example (#352)

Add example for MCP servers embedded inside a CLI tool and update
example validator count.

## Motivation and Context
Document how to model CLI-embedded MCP servers using existing
packages/arguments, per discussion
[#274](https://github.com/modelcontextprotocol/registry/discussions/274).
No schema changes.

## How Has This Been Tested?
- Ran validators: schemas valid; 11/11 examples pass.
- Scripts: ./tools/validate-schemas.sh, ./tools/validate-examples.sh

## Breaking Changes
None.

## 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)
- [x] Documentation update

## Checklist
- [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
- [ ] I have added appropriate error handling
- [x] I have added or updated documentation as needed

## Additional context
Startup reference: [Agentic integrations - Snyk MCP
Server](https://docs.snyk.io/integrations/developer-guardrails-for-agentic-workflows)

---------

Co-authored-by: Adam Jones <adamj@anthropic.com>
Co-authored-by: adam jones <adamj+git@anthropic.com>

tools/validate-examples/main.go

@@ -24,7 +24,7 @@ const (
 	// IMPORTANT: Only change this count if you have intentionally added or removed examples
 	// from the examples.md file. This check prevents accidental formatting changes from
 	// causing examples to be skipped during validation.
-	expectedExampleCount = 11
+	expectedExampleCount = 12
 )
 
 func main() {