Add more validation for free-form server fields (#272)

<!-- Provide a brief summary of your changes -->
The changes are intended to create validators for all the free-form
fields. Please find the details of the validation of different field
below.

- Repository.Source: only github and gitlab is accepted.
- Repository.Url - It should be a valid github or gitlab URL. Created
regex for both.
- Server.Name - Max 200 char can be there. Reverse domain name
verification is part of another PR (not owned by me).
- Package.Name - Max 200 char and no spaces.
- Server.Description - Max 100 char.
- Remote.Url - It should be valid URL.

## Motivation and Context
<!-- Why is this change needed? What problem does it solve? -->
The motivation was to make the code clean and add base code for more
validator for different objects like Repository etc.
https://github.com/modelcontextprotocol/registry/issues/97

## How Has This Been Tested?
It's tested via UTs. Added UT's for all the validations.

## Breaking Changes
Yes

## 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)
- [ ] New feature (non-breaking change which adds functionality)
- [x] 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
- [x] New and existing tests pass locally
- [x] I have added appropriate error handling
- [ ] I have added or updated documentation as needed

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

internal/validators/validators.go

@@ -0,0 +1,124 @@
+package validators
+
+import (
+	"fmt"
+
+	"github.com/modelcontextprotocol/registry/internal/model"
+)
+
+// ServerValidator validates server details
+type ServerValidator struct {
+	*RepositoryValidator // Embedded RepositoryValidator for repository validation
+}
+
+// Validate checks if the server details are valid
+func (v *ServerValidator) Validate(obj *model.ServerDetail) error {
+	if err := v.RepositoryValidator.Validate(&obj.Repository); err != nil {
+		return err
+	}
+	return nil
+}
+
+// NewServerValidator creates a new ServerValidator instance
+func NewServerValidator() *ServerValidator {
+	return &ServerValidator{
+		RepositoryValidator: NewRepositoryValidator(),
+	}
+}
+
+// RepositoryValidator validates repository details
+type RepositoryValidator struct {
+	validSources map[RepositorySource]bool
+}
+
+// Validate checks if the repository details are valid
+func (rv *RepositoryValidator) Validate(obj *model.Repository) error {
+	// Skip validation for empty repository (optional field)
+	if obj.URL == "" && obj.Source == "" {
+		return nil
+	}
+
+	// validate the repository source
+	repoSource := RepositorySource(obj.Source)
+	if !IsValidRepositoryURL(repoSource, obj.URL) {
+		return fmt.Errorf("%w: %s", ErrInvalidRepositoryURL, obj.URL)
+	}
+
+	return nil
+}
+
+// NewRepositoryValidator creates a new RepositoryValidator instance
+func NewRepositoryValidator() *RepositoryValidator {
+	return &RepositoryValidator{
+		validSources: map[RepositorySource]bool{SourceGitHub: true, SourceGitLab: true},
+	}
+}
+
+// PackageValidator validates package details
+type PackageValidator struct{}
+
+// Validate checks if the package details are valid
+func (pv *PackageValidator) Validate(obj *model.Package) error {
+	if !HasNoSpaces(obj.Name) {
+		return ErrPackageNameHasSpaces
+	}
+
+	return nil
+}
+
+// NewPackageValidator creates a new PackageValidator instance
+func NewPackageValidator() *PackageValidator {
+	return &PackageValidator{}
+}
+
+// RemoteValidator validates remote connection details
+type RemoteValidator struct{}
+
+// Validate checks if the remote connection details are valid
+func (rv *RemoteValidator) Validate(obj *model.Remote) error {
+	if !IsValidURL(obj.URL) {
+		return fmt.Errorf("%w: %s", ErrInvalidRemoteURL, obj.URL)
+	}
+	return nil
+}
+
+// NewRemoteValidator creates a new RemoteValidator instance
+func NewRemoteValidator() *RemoteValidator {
+	return &RemoteValidator{}
+}
+
+// ObjectValidator aggregates multiple validators for different object types
+// This allows for a single entry point to validate complex objects that may contain multiple fields
+// that need validation.
+type ObjectValidator struct {
+	ServerValidator  *ServerValidator
+	PackageValidator *PackageValidator
+	RemoteValidator  *RemoteValidator
+}
+
+func NewObjectValidator() *ObjectValidator {
+	return &ObjectValidator{
+		ServerValidator:  NewServerValidator(),
+		PackageValidator: NewPackageValidator(),
+		RemoteValidator:  NewRemoteValidator(),
+	}
+}
+
+func (ov *ObjectValidator) Validate(obj *model.ServerDetail) error {
+	if err := ov.ServerValidator.Validate(obj); err != nil {
+		return err
+	}
+
+	for _, pkg := range obj.Packages {
+		if err := ov.PackageValidator.Validate(&pkg); err != nil {
+			return err
+		}
+	}
+
+	for _, remote := range obj.Remotes {
+		if err := ov.RemoteValidator.Validate(&remote); err != nil {
+			return err
+		}
+	}
+	return nil
+}