feat(viewer): add visual image rotation (90° steps)

[vladopol]

Summary

Adds rotate left / rotate right buttons to the image viewer toolbar for JPEG, PNG and WebP files.

• Two inline toolbar buttons: Rotate counterclockwise (↺) and Rotate clockwise (↻)
• Visual-only rotation via CSS transform: rotate() — no file modification
• Smooth 0.2s CSS transition
• Rotation resets automatically when navigating to the next/previous image
• Zoom is reset on each rotation step
• Buttons are shown only for image files (jpeg/png/webp), not for video/audio

Motivation

When a photo is taken or shared with incorrect orientation (e.g. portrait vs landscape), there is currently no way to adjust the view without leaving the viewer. This PR addresses issues #1846, #2804, #327, #65 with a minimal, non-destructive implementation.

Screenshots

Before	After
No rotation controls	↺ ↻ buttons in toolbar

Test plan

• Open a JPEG/PNG/WebP image in the viewer
• Rotate right: image rotates 90° clockwise with smooth animation
• Rotate left: image rotates 90° counterclockwise
• After 4 clicks in one direction the image is back to original
• Navigate to next/previous image: rotation resets to 0°
• Buttons do NOT appear for video or audio files
• Zoom still works after rotation

Notes

This is a visual-only rotation. It does not modify the file or EXIF data. A separate feature (with file write permission) could be added to persist the rotation — but that is out of scope for this PR.