feat(examples): add delegated access examples with @grant decorator

[Larry-Osakwe]

Summary

• Add delegated_access example for mcp-fastmcp package demonstrating GitHub API integration
• Add delegated_access example for mcp package (low-level integration with AccessContext as function parameter)
• Remove commented-out @grant stubs from hello_world examples
• Update hello_world READMEs to link to the full delegated_access examples
• Add httpx and fastmcp to dev dependencies for example testing

Examples Structure

packages/mcp/examples/
├── hello_world_server/    # Basic auth (cleaned up)
└── delegated_access/      # Full @grant example (NEW)

packages/mcp-fastmcp/examples/
├── hello_world_server/    # Basic auth (cleaned up)
└── delegated_access/      # Full @grant example

Key Features Demonstrated

• AuthProvider setup with ClientSecret credentials
• @grant decorator for token exchange
• AccessContext for accessing exchanged tokens
• Comprehensive error handling (has_errors(), get_errors(), has_resource_error(), etc.)
• GitHub API integration as a real-world example

Closes

AGE-17