[UX]: Missing regenerate/back-to-input flow after quiz generation

### Feature and its Use Cases

After quiz generation completes, users can edit individual questions or export (Google Form / PDF).

However, there is no clear way to:
- Regenerate the full quiz with same parameters
- Go back to the input screen while preserving content
- Adjust difficulty and regenerate
- Retry generation without refreshing the page

Given that generation may take several minutes and question quality may vary, users may need an iteration loop.

### Current Behavior

- Input → Generate → Review → Export
- If unsatisfied, refresh page and re-enter everything

### Expected Behavior
## Proposed UI (Mockup)

**After Quiz Generation:**

┌─────────────────────────────────────────────────┐
│ ← Back to Input 🔄 Regenerate Quiz Export │
│ │
│ Difficulty: [Easy] [Medium ✓] [Hard] │
│ Questions: [5] [10 ✓] [15] [20] │
│ │
│ Question 1: What is... │
│ [Edit] [Delete] [Regenerate This One] │
│ ... │
└─────────────────────────────────────────────────┘
Consider adding:
- "Regenerate Quiz" action
- "Back to Input" navigation with preserved state
- Optional: difficulty adjustment post-generation

This would improve usability and align with modern AI-assisted workflows.

### Additional Context

### Related Work

- PR #383 allows editing/shuffling individual questions
- Issue #384 fixed redirect behavior after generation
- Issue #392 explores adaptive difficulty

However, none address full quiz regeneration or preserving input state for iteration.

### Code of Conduct

- [x] I have joined the [Discord server](https://discord.gg/hjUhu33uAn) and will post updates there
- [x] I have searched existing issues to avoid duplicates