docs: update windowing sizing

[ajpinedam]

GitHub Issue: closes #22206

PR Type:

• 📚 Documentation content changes

What is the current behavior? 🤔

What is the new behavior? 🚀

PR Checklist ✅

Please check if your PR fulfills the following requirements:

• 📝 Commits must be following the Conventional Commits specification.
• 🧪 Added Runtime tests, UI tests, or a manual test sample for the changes have been added (for bug fixes / features) (if applicable)
• 📚 Docs have been added/updated which fit documentation template (for bug fixes / features)
• 🖼️ Validated PR Screenshots Compare Test Run results.
• ❗ Contains NO breaking changes

Other information ℹ️

[Copilot]

Pull request overview

This PR adds documentation for configuring fixed window sizes and disabling window resizing on desktop platforms using the OverlappedPresenter API. The documentation includes code samples showing how to set window dimensions and prevent resizing in both standard applications and those using Uno Navigation.

Key Changes:

• Added new section "Fixing a window size and preventing resizing" with configuration examples
• Included guidance for apps using Uno Navigation with timing considerations
• Provided code samples demonstrating OverlappedPresenter configuration in OnLaunched

⚠️ Important: The PR description is missing a proper issue reference (shows "closes #" without an issue number). According to repository guidelines (CodingGuidelineID: 1000001), every PR must reference a GitHub issue using the fully qualified format: Fixes https://github.com/unoplatform/uno/issues/#<ISSUE_NUMBER> or include a note if this is approved internal maintenance.

[unodevops]

🤖 Your Docs stage site is ready! Visit it here: https://unodocsprstaging.z13.web.core.windows.net/pr-22225/docs/index.html

[unodevops]

🤖 Your Docs stage site is ready! Visit it here: https://unodocsprstaging.z13.web.core.windows.net/pr-22225/docs/index.html