feat: Add support for MCP Bundles (MCPB) in registry (#295)

## Motivation and Context
- Add MCPB as a new registry_name option
- Add file_hashes field to package model for integrity verification
- Implement URL validation restricting MCPB packages to GitHub/GitLab
hosts
- Require SHA-256 hash for all MCPB packages
- Add example MCPB package in documentation
- Update schemas and OpenAPI specification

See issue #260

## How Has This Been Tested?
<!-- Have you tested this in a real application? Which scenarios were
tested? -->

## Breaking Changes
N/A, registry has not yet been launched

## 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)
- [ ] Breaking change (fix or feature that would cause existing
functionality to change)
- [ ] 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)
- [ ] My code follows the repository's style guidelines
- [ ] New and existing tests pass locally
- [ ] I have added appropriate error handling
- [x] I have added or updated documentation as needed

---------

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

internal/validators/validators.go

@@ -59,7 +59,7 @@ type PackageValidator struct{}
 
 // Validate checks if the package details are valid
 func (pv *PackageValidator) Validate(obj *model.Package) error {
-	if !HasNoSpaces(obj.Name) {
+	if !HasNoSpaces(obj.Identifier) {
 		return ErrPackageNameHasSpaces
 	}
 

internal/validators/validators_test.go

@@ -31,8 +31,9 @@ func TestObjectValidator_Validate(t *testing.T) {
 				},
 				Packages: []model.Package{
 					{
-						Name:         "test-package",
-						RegistryName: "npm",
+						Identifier:      "test-package",
+						RegistryType:    "npm",
+						RegistryBaseURL: "https://registry.npmjs.org",
 					},
 				},
 				Remotes: []model.Remote{
@@ -102,8 +103,9 @@ func TestObjectValidator_Validate(t *testing.T) {
 				},
 				Packages: []model.Package{
 					{
-						Name:         "test package with spaces",
-						RegistryName: "npm",
+						Identifier:      "test package with spaces",
+						RegistryType:    "npm",
+						RegistryBaseURL: "https://registry.npmjs.org",
 					},
 				},
 			},
@@ -123,12 +125,14 @@ func TestObjectValidator_Validate(t *testing.T) {
 				},
 				Packages: []model.Package{
 					{
-						Name:         "valid-package",
-						RegistryName: "npm",
+						Identifier:      "valid-package",
+						RegistryType:    "npm",
+						RegistryBaseURL: "https://registry.npmjs.org",
 					},
 					{
-						Name:         "invalid package", // Has space
-						RegistryName: "pip",
+						Identifier:      "invalid package", // Has space
+						RegistryType:    "pypi",
+						RegistryBaseURL: "https://pypi.org",
 					},
 				},
 			},