Refactor shared animation logic into useFortuneAnimation hook

[google-labs-jules]

Extracted duplicated animation logic from FortuneBar and FortuneWheel into a new shared hook useFortuneAnimation in lib/src/core/animations.dart.
This hook manages:

• AnimationController creation
• CurvedAnimation creation
• Logic to run animation on start (if enabled)
• Logic to listen to selection stream and run animation
• Updating selectedIndex state

Updated FortuneBar and FortuneWheel to use this hook and access the controller, animation, and selectedIndex from the returned FortuneAnimation object.
Verified visually that logic is preserved and files are updated correctly. Tests could not be run due to missing Flutter environment, but the refactoring is a straightforward extraction of existing logic.

---

PR created automatically by Jules for task 10603008920263147183 started by @kevlatus

[google-labs-jules]

👋 Jules, reporting for duty! I'm here to lend a hand with this pull request.

When you start a review, I'll add a 👀 emoji to each comment to let you know I've read it. I'll focus on feedback directed at me and will do my best to stay out of conversations between you and other bots or reviewers to keep the noise down.

I'll push a commit with your requested changes shortly after. Please note there might be a delay between these steps, but rest assured I'm on the job!

For more direct control, you can switch me to Reactive Mode. When this mode is on, I will only act on comments where you specifically mention me with @jules. You can find this option in the Pull Request section of your global Jules UI settings. You can always switch back!

New to Jules? Learn more at jules.google/docs.

---

For security, I will only act on instructions from the user who triggered this task.