Resolve all lints and deprecation warnings

lib/widgets/tip_card.dart

@@ -25,12 +25,13 @@ class TipCard extends StatelessWidget {
       decoration: BoxDecoration(
         color: theme.cardColor,
         borderRadius: BorderRadius.circular(16),
-        border:
-            isDark ? Border.all(color: Colors.white.withOpacity(0.05)) : null,
+        border: isDark
+            ? Border.all(color: Colors.white.withValues(alpha: 0.05))
+            : null,
         boxShadow: [
           BoxShadow(
             color: (isDark ? Colors.black : AppColors.charcoal)
-                .withOpacity(0.05),
+                .withValues(alpha: 0.05),
             blurRadius: 10,
             offset: const Offset(0, 4),
           ),
@@ -43,7 +44,7 @@ class TipCard extends StatelessWidget {
             width: 40,
             height: 40,
             decoration: BoxDecoration(
-              color: AppColors.sageGreen.withOpacity(isDark ? 0.2 : 0.15),
+              color: AppColors.sageGreen.withValues(alpha: isDark ? 0.2 : 0.15),
               borderRadius: BorderRadius.circular(10),
             ),
             child: const Icon(