setZoomLevel() / setZoomFactor() is silently ignored before the first navigation in the isolated and manual zoom modes

### Preflight Checklist

- [x] I have read the [Contributing Guidelines](https://github.com/electron/electron/blob/main/CONTRIBUTING.md) for this project.
- [x] I agree to follow the [Code of Conduct](https://github.com/electron/electron/blob/main/CODE_OF_CONDUCT.md) that this project adheres to.
- [x] I have searched the [issue tracker](https://www.github.com/electron/electron/issues) for a bug report that matches the one I want to file, without success.

### Electron Version

45.0.0-nightly.20260826 (current `main`, local build)

### What operating system(s) are you using?

macOS

### Operating System Version

macOS 26.5

### What arch are you using?

arm64

### Last Known Working Electron version

None known

### Does the issue also appear in Chromium / Google Chrome?

No

### Expected Behavior

A zoom level set before the first navigation commits is applied once the page loads, in the zoom
modes that are meant to persist (`isolated` and `manual`) – the same way
`webPreferences: { zoomMode: 'isolated', zoomFactor: 1.5 }` already behaves.

### Actual Behavior

The call is silently dropped – no error, no return value, and `getZoomFactor()` stays at `1`:

```js
const w = new BrowserWindow({ webPreferences: { zoomMode: 'isolated' } })
w.webContents.setZoomFactor(1.5) // silently dropped
await w.loadURL('https://example.com')
w.webContents.getZoomFactor() // 1 (expected 1.5)
```

`WebContentsZoomController::SetZoomLevel()` bails out on `!IsRenderFrameLive()` (no frame is live
before the first navigation commits), and the JS binding discards its `bool` result, so nothing
surfaces to the app. Expressing the same intent through web preferences does work, so the two
spellings of one intent disagree.

### Testcase Gist URL

_No response_

### Additional Information

The snippet above is the complete reproduction. The affected API surface is Electron-specific
(`webContents.setZoomLevel()` / `setZoomFactor()` and the `zoomMode` web preference), so there is
no Chromium equivalent to compare against. Workaround: pass the initial factor via
`webPreferences: { zoomFactor }` instead of calling the setter before load.

Fix with regression specs: #53226.

Start with WebContentsZoomController::SetZoomLevel() and the JavaScript binding that exposes webContents.setZoomLevel() and setZoomFactor(). Use the regression specs planned in #53226 to verify that pre-navigation setters persist in isolated and manual zoom modes and that getZoomFactor() reports the requested value after loading.

Written by the indexing model from the issue text.