When the parent agent uses a composite toolset like hermes-cli, calling
delegate_task with individual toolsets (e.g. web, terminal) resulted in
zero tools because the name-based intersection failed: 'web' != 'hermes-cli'.
Add _expand_parent_toolsets() which collects all tool names from parent
toolsets, then recognises any individual toolset whose tools are a subset
of the parent's available tools. This allows delegate_task(toolsets=['web'])
to work correctly when the parent has hermes-cli enabled.
Fixes#19447
