* feat(chat): add message fork action
Use a Y-shaped repo-forked icon in fork UI and expose the current-tail /fork action in the last message meta action row instead of the input toolbar. Keep terminal fork commands out of optimistic run/thinking state so no model activity is implied.
* fix(chat): debounce fork message action
* fix chat session click after fork
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Co-authored-by: Zhicheng Han <zhicheng.han@mathematik.uni-goettingen.de>
ekko