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>

scripts/test_publish.sh

@@ -91,8 +91,9 @@ cat > "$PAYLOAD_FILE" << EOF
   },
   "packages": [
     {
+      "package_type": "javascript",
       "registry_name": "npm",
-      "name": "test-mcp-server",
+      "identifier": "test-mcp-server",
       "version": "1.0.$(date +%s)",
       "runtime_hint": "node",
       "runtime_arguments": [