Improve dialog EDT behavior in BrowseCoursesDialog

[meanmail]

Overview

Dialog validation is being triggered directly on EDT from callbacks without proper modality state, potentially causing freezes.

Location

File: intellij-plugin/hs-core/src/org/hyperskill/academy/learning/newproject/ui/BrowseCoursesDialog.kt
Lines: 45-67

Problems

1. Line 47: panel.doValidation() is called directly on EDT from pluginLoaded callback - this could trigger heavy operations
2. Line 59: panel.doValidation() is called on EDT from notification listener without proper modality state
3. TODO comment on lines 60-63 indicates there's a known IDE freeze issue when installing/uninstalling plugins

What needs to be fixed

• Investigate what panel.doValidation() does and move heavy operations to background
• Use proper modality state for invokeLater calls (line 51 has it, line 59 doesn't)
• Add progress indicators for long-running validation
• Consider debouncing validation calls to prevent multiple rapid invocations
• Fix the TODO about IDE freezes during plugin install/uninstall

Tests understanding of

• Dialog lifecycle and EDT requirements
• ApplicationManager.getApplication().invokeLater() with modality states
• Progress indicators for background operations
• Plugin lifecycle events
• Debouncing/throttling UI updates

Validation

• Install/uninstall plugins while dialog is open
• Ensure no freezes occur
• Verify validation still works correctly
• Test with slow network/API responses

Estimated time

3-4 hours