When a subagent was spawned while the parent had runtime-modified
settings (fast mode, thinking, etc.), the subagent would start with
defaults from `AgentSettings` instead of inheriting the parent's current
values.
This adds `inherit_parent_settings` as a single place in
`Thread::new_subagent` that copies all runtime-mutable settings from the
parent:
- `speed`
- `thinking_enabled`
- `thinking_effort`
- `summarization_model`
- `profile_id`
These are the same properties that `set_*` methods already propagate to
`running_subagents` — this fix ensures they're also inherited at
creation time.
cc @benbrandt
Release Notes:
- N/A
Nathan Sobo
f548dfc604