refactor: modernize timeline view, css, and localization

- Refactor ActivityLogTimelineTableAction for better null handling and strict typing
- Update ActivitiesRelationManager to include causer activities
- Modernize timeline.blade.php:
  - Replace all Tailwind classes with custom CSS
  - Use x-heroicon components for better alignment
  - Implement full localization for empty states and changes
- Refactor filament-activity-log.css:
  - Remove comments and organize structure
  - Implement dynamic theme colors using Filament CSS variables
- Add missing localization keys (old, new, empty_state) to all languages

Author: AlizHarb

README.md

@@ -96,6 +96,14 @@ public function panel(Panel $panel): Panel
 php artisan vendor:publish --tag="filament-activity-log-config"
 ```
 
+### Step 4: Publish Assets (Optional)
+
+If you need to customize the CSS or other assets:
+
+```bash
+php artisan vendor:publish --tag="filament-activity-log-styles"
+```
+
 ---
 
 ## 🎯 Quick Start