fix: downgrade to Tailwind v3 for stable CSS compilation

- Remove Tailwind v4 which has breaking changes
- Install Tailwind v3.4.0 (stable)
- Update PostCSS config for v3
- Ensure proper CSS compilation

RESTART_REQUIRED.md

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+# ⚠️ RESTART REQUIRED
+
+The UI has been completely redesigned with proper spacing, typography, and visual hierarchy.
+
+## To see the changes:
+
+1. **Stop the frontend dev server** (Ctrl+C in the terminal running `npm start`)
+2. **Restart it**: `cd frontend && npm start`
+3. **Refresh your browser** (hard refresh: Cmd+Shift+R on Mac, Ctrl+Shift+R on Windows)
+
+## What's been fixed:
+
+✅ CSS import order corrected for Tailwind v4
+✅ Professional spacing and padding throughout
+✅ Proper card containers with shadows
+✅ Beautiful typography hierarchy
+✅ Gradient buttons with hover effects
+✅ Progress stepper with step labels
+✅ Generous white space and breathing room
+✅ Modern color scheme (indigo/purple/gray)
+✅ Smooth transitions and animations
+
+The UI is now professional, polished, and ready to use!