Fixes an issue where toggling an MCP server on/off in Settings → AI →
MCP Servers does not update the toggle state in the UI immediately.

## Root Cause

There were two issues:

1. `ContextServerStore::update_server_state()` and `remove_server()`
emitted `ServerStatusChangedEvent` but did not call `cx.notify()`, so
Settings UI observers were not informed to re-render.

2. `render_toggle_switch()` was bound to `is_running` (runtime status)
instead of `is_enabled` (settings state).

## Solution

- Add `cx.notify()` in both methods after emitting the status event.
- Change toggle to read `settings.enabled()` and rename parameter from
`is_running` to `is_enabled`.

## Testing

- `cargo check -p settings_ui -p project` passes.
- `cargo fmt --check` passes.
- Manual verification: open Settings → AI → MCP Servers, toggle a
server, observe immediate UI update.

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Release Notes:

- Fixed MCP server toggle not updating immediately in Settings UI.

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Co-authored-by: dino <dinojoaocosta@gmail.com>