No minimum window size in App UI - Icon Browser, Navigation Graph and DevTools windows

Reproduction steps:
1. Create a new project
2. Install App UI Package via Package Manager or AI button in the top Editor toolbar
3. Window > App UI > Icon Browser
4. Resize the window to the smallest possible size and observe

Actual result: None of the window features are visible
Expected result: Window has minimum size bounds to ensure most important features remain visible

Reproducible with: 1.3.1 (6000.0.65f1), 2.1.3 (6000.0.65f1, 6000.3.3f1, 6000.4.0b3, 6000.5.0a4)

Reproduced on: macOS Tahoe 26.2 (M4)