Context

The git panel's context menu caused visual jitter (flickering/jumping)
when opened via right-click on a tracked file. The root cause was in
`dispatch_context()`: it used `self.focus_handle == focused` to check if
the panel itself was directly focused, but when a context menu opened,
focus moved to the menu (a child element), causing the `"menu"` and
`"ChangesList"` key contexts to be dropped. This triggered a re-render
with different keybindings, which re-added them, creating a loop of
jitter.

The fix replaces the direct focus equality check with
`self.focus_handle.contains_focused(window, cx)`, which returns `true`
when any child element (including the context menu) holds focus within
the panel's focus tree. This is consistent with how other panels
(project panel, outline panel, collab panel) handle focus-based dispatch
contexts.

Closes #51813

## Demo

**Before fix:**




https://github.com/user-attachments/assets/e18d49b2-72a6-4411-8ec5-519e36628f29


**After fix:**



https://github.com/user-attachments/assets/94c936d2-1e81-4d28-a86a-8b1ed76ddde1



## How to Review

This is a small, focused change in a single file:
`crates/git_ui/src/git_panel.rs`.

1. **The fix** (~line 974): `dispatch_context()` method — the old code
checked direct focus equality (`self.focus_handle == focused`), the new
code uses `self.focus_handle.contains_focused(window, cx)` and
restructures the conditionals so `CommitEditor` is checked first via
`if/else if`.
2. **The test** (~line 7871): `test_dispatch_context_with_focus_states`
— verifies 4 focus state transitions: commit editor focused, changes
list focused, back to commit editor, and back to changes list. Each case
asserts the correct key contexts are present/absent.

## Self-Review Checklist

- [x] I've reviewed my own diff for quality, security, and reliability
- [ ] Unsafe blocks (if any) have justifying comments
- [x] The content is consistent with the [UI/UX
checklist](https://github.com/zed-industries/zed/blob/main/CONTRIBUTING.md#uiux-checklist)
- [x] Tests cover the new/changed behavior
- [x] Performance impact has been considered and is acceptable

Release Notes:

- Fixed git panel context menu jitter caused by keybinding dispatch
context flickering when right-clicking on tracked files (#51813)