🧹 Remove unused_variables allowance in run_native_window

[undivisible]

🎯 What: The #[allow(unused_variables)] attribute was removed from run_native_window in src/shell/main_desktop.rs, and unused variable warnings were addressed by conditionally using let _ = ....
💡 Why: Relying on #[allow(unused_variables)] globally disables helpful compiler lints. Explicitly silencing specific variables improves readability and explicitly declares developer intent.
✅ Verification: Verified via rustc that the file compiles cleanly with no unused variable warnings on default target compilation configurations.
✨ Result: A cleaner codebase where compiler diagnostics can be fully trusted to catch actual unused variables within the function body.

---

PR created automatically by Jules for task 16819373064959425216 started by @undivisible

[google-labs-jules]

👋 Jules, reporting for duty! I'm here to lend a hand with this pull request.

When you start a review, I'll add a 👀 emoji to each comment to let you know I've read it. I'll focus on feedback directed at me and will do my best to stay out of conversations between you and other bots or reviewers to keep the noise down.

I'll push a commit with your requested changes shortly after. Please note there might be a delay between these steps, but rest assured I'm on the job!

For more direct control, you can switch me to Reactive Mode. When this mode is on, I will only act on comments where you specifically mention me with @jules. You can find this option in the Pull Request section of your global Jules UI settings. You can always switch back!

New to Jules? Learn more at jules.google/docs.

---

For security, I will only act on instructions from the user who triggered this task.