Add empty state illustration when History or Rules lists are empty

[vssinghh]

🎯 Summary

When the History or Rules screens have no items, the user sees a blank screen. Add a friendly empty state with an icon and message to guide the user.

📍 Where to Look

• app/src/main/java/com/hush/app/ui/screens/history/HistoryScreen.kt — The LazyColumn for history logs
• app/src/main/java/com/hush/app/ui/screens/rules/RulesScreen.kt — The rules list

✅ What to Do

1. Check if the list is empty before rendering the LazyColumn
2. If empty, show a centered column with:
   • A Material icon (e.g., Icons.Outlined.Notifications for History, Icons.Outlined.Rule for Rules)
   • A friendly title like "No notifications yet" or "No rules created"
   • A subtitle with guidance like "Filtered notifications will appear here" or "Say something in Chat to create your first rule"
3. Use MaterialTheme.colorScheme.onSurfaceVariant for muted text styling

🧪 How to Verify

• Fresh install or clear app data
• Open History tab — should show the empty state illustration
• Open Rules tab — should show the empty state illustration
• Create a rule — the empty state should disappear and the rule should appear

💡 Hints

• Use a simple if/else around the LazyColumn — no complex logic needed
• Look at how other Material 3 apps handle empty states for design inspiration

A small polish that makes the app feel much more professional! 🙌