[FEAT] Add Side-by-Side Before/After View for Transformed Clips

[Emmzyemms]

Description:
The transform result page needs a compelling side-by-side comparison UI showing the original clip alongside the AI-transformed version.

Acceptance Criteria:

• Create components/transform/TransformResult.tsx
• Drag-to-compare slider between original and transformed video frames
• Both videos are synchronised: play/pause/scrub affects both simultaneously
• Style watermark shown on the transformed side (e.g. "✨ Anime Style")
• Fullscreen toggle available
• "Share Comparison" generates a public share link (Issue feat: Frontend: [Component] Drag & Drop Video Upload Zone #78) that shows this side-by-side
• Storybook story with mock video URLs

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