[Bug] GeneralSection handleNotificationToggle fires IPC call inside setState updater

## Problem

`GeneralSection.handleNotificationToggle` performs an IPC side-effect **inside** a `setState` updater. React explicitly disallows this — state updaters must be pure functions. In React Strict Mode (enabled in dev), updaters are invoked twice to detect impurity, which means `window.clawwork.updateSettings(...)` fires **twice** for every notification toggle, persisting the same change twice and doubling the IPC round-trip cost.

## Location

**File:** `packages/desktop/src/renderer/layouts/Settings/sections/GeneralSection.tsx:102-111`

```typescript
const handleNotificationToggle = useCallback(
(key: 'taskComplete' | 'approvalRequest' | 'gatewayDisconnect', value: boolean) => {
setNotifyState((prev) => {
const next = { ...prev, [key]: value };
window.clawwork.updateSettings({ notifications: next }); // ← side effect in updater
return next;
});
},
[],
);
```

## Fix Approach

Compute the new state outside the updater, then dispatch both the state update and the IPC call as separate effects:

```typescript
const handleNotificationToggle = useCallback(
(key: 'taskComplete' | 'approvalRequest' | 'gatewayDisconnect', value: boolean) => {
const next = { ...notifyState, [key]: value };
setNotifyState(next);
window.clawwork.updateSettings({ notifications: next });
},
[notifyState],
);
```

Or, if you want to avoid re-creating the callback on every state change, keep a ref that tracks the latest `notifyState` and use it inside the callback.

## Verification

1. Run `pnpm check` — must pass.
2. Manual: in dev mode (Strict Mode enabled), toggle a notification switch and confirm only a single IPC call fires in the main-process logs.

## Context

- **WG:** UI & Design System
- **Priority:** Low (good first issue)
- **Estimated effort:** 10-15 minutes

Open packages/desktop/src/renderer/layouts/Settings/sections/GeneralSection.tsx at lines 102-111 and inspect GeneralSection.handleNotificationToggle. Run pnpm check, then use dev mode with Strict Mode enabled to toggle a notification switch and confirm the main-process logs show only one IPC call.

Written by the indexing model from the issue text.