[Feature Request] Add arbitrary-angle rotation (fine-tune rotation) support

Windows OS version

Windows 11 25H2

ImageGlass version

v9.5.0.515

ImageGlass release

Classic

1️⃣ Describe the feature

• Currently ImageGlass supports 90°/180°/270° fixed rotation only.
• I propose adding an arbitrary-angle rotation (or fine-tune rotation) feature.
• This allows users to rotate an image by any degree (e.g., 1.5°, 15°, 30.2°) via a slider, input box, or mouse drag.
• It would greatly help to straighten crooked photos or adjust composition precisely.
• Should be non-destructive (or apply to saved copy, like existing rotation).

2️⃣ How to use feature

1. In the edit/rotation menu, add a new option "Arbitrary Rotation" or "Fine-tune Angle".
2. A dialog or panel appears with:
   • A slider (e.g., -180° to +180°)
   • A numeric input box to type exact degrees
   • Live preview of the rotated image
3. Click "Apply" to confirm or "Cancel" to revert.
4. Alternatively, allow rotating by dragging a handle/angle wheel directly on the image.

3️⃣ Additional context

No response

Start at the existing edit/rotation menu and the implementation of the fixed 90°, 180°, and 270° rotations. Define how an arbitrary-angle dialog or panel should provide slider or numeric input, live preview, Apply, and Cancel while preserving the existing save behavior. Done means users can fine-tune an image angle and confirm or revert the result.