feat: implement swipe back gesture with visual indicator

[EduTiyo]

Summary

Adds native-feeling trackpad back gesture navigation (similar to Safari and Chrome on macOS), allowing users to return from the project editor to the project list via a two-finger horizontal swipe.

Changes

• useTrackpadBack hook:
  • Detects two-finger horizontal swipes (wheel with negative deltaX) on macOS trackpads.
  • Seamlessly integrates with the existing isDirty state and confirmation dialog (UnsavedChangesDialog) before discarding unsaved edits.
  • Prevents conflict with horizontally scrollable inner elements (isInsideHorizontallyScrollable) and ignores vertical scrolling.
  • Adds browser shortcut companions: ⌘ + [ (macOS), Alt + ← (cross-platform), and mouse button 4 (auxclick).
  • Includes a momentum cooldown and state reset lifecycle to ensure the gesture can be triggered reliably and repeatedly across sessions.
• SwipeBackIndicator component:
  • Unified concentric SVG geometry with circular progress tracking ((24, 24) center coordinates).
  • Smoothly slides out from the left screen edge and visually tracks gesture progress from 0% to 100%.
  • Highlights upon threshold completion with a brief confirmation pause (~110ms) before committing navigation.
• index.css:
  • Adds overscroll-behavior-x: none; on html, body, #root to prevent WKWebView horizontal rubber-band elastic bounce.

Verification

• Open any project in the editor and swipe right with two fingers on trackpad -> smoothly transitions back to project list.
• Modify a field without saving and swipe right -> triggers UnsavedChangesDialog properly.
• Open and navigate back repeatedly across multiple projects without restarting the app.
• Verified build passes with zero errors: npm run build.