feat: add short SDK resource methods

[bardonadam]

Summary

• add wrapper resources with short methods (notifications.send, live_activities.start/update/end)
• keep legacy snake_case methods as backward-compatible aliases
• preserve passthrough access to generated methods via method_missing
• update README examples to use short methods
• add test assertions for new methods

Validation

• bundle exec rake test (not runnable here: missing gem dependencies in local Ruby env)
• ruby -c on changed Ruby files