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>

docs/reference/server-json/server.schema.json

@@ -396,6 +396,13 @@
           "minLength": 1,
           "maxLength": 100
         },
+        "title": {
+          "type": "string",
+          "description": "Optional human-readable title or display name for the MCP server. MCP subregistries or clients MAY choose to use this for display purposes.",
+          "example": "Weather API",
+          "minLength": 1,
+          "maxLength": 100
+        },
         "repository": {
           "$ref": "#/definitions/Repository",
           "description": "Optional repository metadata for the MCP server source code. Recommended for transparency and security inspection."