Add optional title field to server.json schema (#608)

## Summary

Introduces a new optional `title` field for MCP servers to provide a
clean, human-readable display name that clients and subregistries can
use for display purposes.

Fixes #606

## Changes

- Added `title` field to `ServerJSON` type (optional, max 100 chars)
- Added validation to reject titles ending with 'MCP Server', 'MCP
server', or 'MCP' suffixes
- Updated JSON schema and OpenAPI specification
- Added comprehensive test coverage for title validation
- Updated all documentation examples to demonstrate the new field

## Validation

The title field:
- Is optional (can be omitted)
- Must not be only whitespace if provided
- Must not end with MCP-related suffixes (case-insensitive)
- Can contain 'MCP' in the middle (e.g., "MCP Weather API" is valid)

Examples:
- ✅ Valid: "GitHub", "Weather API", "Slack Integration"
- ❌ Invalid: "GitHub MCP", "Weather MCP Server", "Slack-MCP"

---------

Co-authored-by: Claude <noreply@anthropic.com>

pkg/api/v0/types.go

@@ -41,6 +41,7 @@ type ServerJSON struct {
 	Schema      string            `json:"$schema" required:"true" minLength:"1"`
 	Name        string            `json:"name" minLength:"1" maxLength:"200"`
 	Description string            `json:"description" minLength:"1" maxLength:"100"`
+	Title       string            `json:"title,omitempty" minLength:"1" maxLength:"100"`
 	Repository  model.Repository  `json:"repository,omitempty"`
 	Version     string            `json:"version"`
 	WebsiteURL  string            `json:"websiteUrl,omitempty"`