feat: improve hook UX and execution model

[garethgeorge]

significant changes are

• hooks are now organized as children of the operation that triggered them in the UI
• the type of hook is now included in the execution details displayed in the UI
• both successful and failed hooks are visible in the UI, sections containing failed child hooks will be expanded by default
• under-the-hood hooks are now tasks and execute with the same semantics re: log capture, error handling, etc.
• improved hook interface -- new hook types can now be easily registered via a registry object, will enable additional hook type support going forward.

Screenshot