Release Notes:
- Made keybindings for agent panel closer to the precedence order used
on Mac. This fixes use of `enter` to add context from the menu triggered
by `@` referencing.
Also, we moved the logic for driving the agentic loop into `Thread` so
that we don't have to re-implement it.
Release Notes:
- N/A
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Co-authored-by: Nathan Sobo <nathan@zed.dev>