docs: add UI style guide documenting no native alerts rule

Documented the project's UI pattern requirements:
- Never use native browser dialogs (alert/confirm/prompt)
- Always use inline React-based confirmations
- Included pattern examples and migration checklist
- Referenced ModerationPanel.tsx for real examples

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude <noreply@anthropic.com>

apps/web/.claude/UI_STYLE_GUIDE.md

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+# UI Style Guide
+
+## Confirmations and Dialogs
+
+**NEVER use native browser dialogs:**
+- ❌ `alert()`
+- ❌ `confirm()`
+- ❌ `prompt()`
+
+**ALWAYS use inline React-based confirmations:**
+- Show confirmation UI in-place using React state
+- Provide Cancel and Confirm buttons
+- Use descriptive warning messages with appropriate emoji (⚠️)
+- Follow the Panda CSS styling system
+- Match the visual style of the surrounding UI
+
+### Pattern: Inline Confirmation
+
+```typescript
+const [confirming, setConfirming] = useState(false)
+
+{!confirming ? (
+  <button onClick={() => setConfirming(true)}>
+    Delete Item
+  </button>
+) : (
+  <div>
+    <div style={{ /* warning styling */ }}>
+      ⚠️ Are you sure you want to delete this item?
+    </div>
+    <div style={{ /* description styling */ }}>
+      This action cannot be undone.
+    </div>
+    <div style={{ display: 'flex', gap: '8px' }}>
+      <button onClick={() => setConfirming(false)}>
+        Cancel
+      </button>
+      <button onClick={handleDelete}>
+        Confirm Delete
+      </button>
+    </div>
+  </div>
+)}
+```
+
+### Real Examples
+
+See `/src/components/nav/ModerationPanel.tsx` for production examples:
+- Transfer ownership confirmation (lines 1793-1929)
+- Unban user confirmation (shows inline warning with Cancel/Confirm)
+
+### Why This Pattern?
+
+1. **Consistency**: Native dialogs look different across browsers and platforms
+2. **Control**: We can style, position, and enhance confirmations to match our design
+3. **Accessibility**: We can add proper ARIA attributes and keyboard navigation
+4. **UX**: Users stay in context rather than being interrupted by modal dialogs
+5. **Testing**: Inline confirmations are easier to test than native browser dialogs
+
+### Migration Checklist
+
+When replacing native dialogs:
+- [ ] Add state variable for confirmation (e.g., `const [confirming, setConfirming] = useState(false)`)
+- [ ] Remove the `confirm()` or `alert()` call from the handler
+- [ ] Replace the original UI with conditional rendering
+- [ ] Show initial state with primary action button
+- [ ] Show confirmation state with warning message + Cancel/Confirm buttons
+- [ ] Ensure Cancel button resets state: `onClick={() => setConfirming(false)}`
+- [ ] Ensure Confirm button performs action and resets state
+- [ ] Add loading states if the action is async
+- [ ] Style to match surrounding UI using Panda CSS
+
+## Styling System
+
+This project uses **Panda CSS**, not Tailwind CSS.
+
+- ❌ Never use Tailwind utility classes (e.g., `className="bg-blue-500"`)
+- ✅ Always use Panda CSS `css()` function
+- ✅ Use Panda's token system (defined in `panda.config.ts`)
+
+See `.claude/CLAUDE.md` for complete Panda CSS documentation.
+
+## Emoji Usage
+
+Emojis are used liberally throughout the UI for visual communication:
+- 👑 Host/owner status
+- ⏳ Waiting states
+- ⚠️ Warnings and confirmations
+- ✅ Success states
+- ❌ Error states
+- 👀 Spectating mode
+- 🎮 Gaming context
+
+Use emojis to enhance clarity, not replace text.