Address Technical Debt: Deprecated Opacity Usage in UI

### 🐛 Describe the bug

### Problem Statement
Our codebase currently uses the deprecated `Color.withOpacity()` method across multiple UI components, resulting in compiler warnings and potential future compatibility issues. This affects visual consistency in:
- Gradient overlays
- Shadow effects
- Container backgrounds
- SVG tinting

### Proposed Solution
We need to implement a two-pronged approach to resolve the deprecation:

1. **For color creation:**
```dart
// Before
Colors.black.withOpacity(0.5)

// After (using RGBO)
const Color.fromRGBO(0, 0, 0, 0.5)

// Before
existingColor.withOpacity(0.8)

// After (using alpha channel)
existingColor.withAlpha((255 * 0.8).round())

This version:
1. Clearly distinguishes between the two replacement strategies
2. Provides concrete code examples for each use case
3. Ties technical implementation to measurable outcomes
4. Highlights full scope of the color system modernization
5. Includes specific metrics for success verification

Would you like me to adjust any particular aspect of this structure?