Windows: main window title is empty, so the taskbar shows no app name

**Describe the bug**
The Buzz main window has no title set. Windows draws taskbar labels from the window caption, so the Buzz taskbar entry renders as an icon with no name next to it.

**Steps to reproduce**
1. Launch Buzz on Windows 11
2. Look at the taskbar entry for Buzz
3. The icon appears with no accompanying app name, unlike every other running application

**Expected behavior**
The taskbar entry should read "Buzz" next to the icon.

**Version and platform**
- Buzz version: 0.5.17
- OS: Windows 11 Pro 25H2, build 26200.9168

**Logs / additional context**
`buzz-desktop`'s `MainWindowTitle` is an empty string (length 0). Comparison of `MainWindowTitle` across running apps on the same machine:

| Process | MainWindowTitle |
|---|---|
| ChatGPT | `ChatGPT` |
| codexbar | `CodexBar Desktop` |
| claude | `Claude` |
| WhatsApp.Root | `WhatsApp` |
| **buzz-desktop** | **``** |

Nothing is suppressing the label — the string simply isn't set. Likely the Tauri window `title` field is unset in the app configuration.