fix(crop-rotate-editor): ignore setState after dispose and color undo/redo with appBarColor

[hm21]

Description

Two crop-rotate editor bugs, fixed in one PR.

#858: Bad state: Cannot add new events after calling close

ScreenResizeDetector.onResizeEnd fires from a 50 ms debounce, and the crop editor responds by scheduling a post-frame callback that calls _updateAllStates() → setState(). If the editor is removed in the frame where that debounce fires, dispose() has already closed rebuildController by the time the callback runs, and rebuildController.add(null) throws. The UI isn't affected, but apps that forward FlutterError.onError to Crashlytics/Sentry report it as a crash.

• The setState overrides of the blur, crop, filter, paint, text and tune editors now return early when the state isn't mounted. The main editor already did this.
• The crop editor's three post-frame callbacks (the two in initState and the one in onResizeEnd) also return early when the state isn't mounted, so they no longer call calcFitToScreen() / _setCropRectBounding() on disposed animation controllers.

#856: undo/redo ignore appBarColor

The undo and redo icons in CropEditorAppbar and TuneEditorAppbar were hardcoded to Colors.white / Colors.white.withAlpha(80). The done button follows appBarColor, so with a light appBarBackground undo and redo disappeared. They now use style.appBarColor (with alpha 80 when disabled), as PaintEditorAppbar already does. kImageEditorAppBarColor is white, so the default look is unchanged. The frosted-glass example designs hardcode white on purpose and are unchanged.

Related Issue: Closes #858, closes #856

Type of Change

• ✨ New feature (non-breaking change which adds functionality)
• 🛠️ Bug fix (non-breaking change which fixes an issue)
• ❌ Breaking change (fix or feature that would cause existing functionality to change)
• 🧹 Code refactor
• ✅ Build configuration change
• 📝 Documentation
• 🗑️ Chore

Tests

• Crop editor: a repro for [Bug]: CropRotateEditor crashes with "Bad state: Cannot add new events after calling close" when the editor is closed while a resize-end callback is pending #858 replaces the editor in the same frame where the initial resize debounce fires. Before the fix it throws the reported StateError.
• Blur, crop, filter, paint, text and tune editors: calling setState after dispose returns normally.
• Crop and tune editors: undo and redo icons use the configured appBarColor.
• All 9 new tests fail against stable and pass with the fix.
• flutter test (674 tests), flutter analyze and dart format pass.