Fix linting issues and code quality improvements

Resolve 62 linting issues identified by flutter analyze, reducing
total issues from 79 to 17. All critical warnings addressed.

Changes:
- Replace deprecated withOpacity() with withValues(alpha:) (25 instances)
- Remove unused imports from 9 files
- Remove unused variables and fields (6 instances)
- Fix Riverpod 3.0 state access violations in settings_page
- Remove unnecessary null-aware operators in navigation_page (6 instances)
- Fix unnecessary type casts in providers (4 instances)
- Remove unused methods: _getDarkMapStyle, _showPermissionDialog
- Simplify hover state management by removing unused _isHovered fields

Remaining 17 issues are info-level style suggestions and defensive
programming patterns that don't impact functionality.

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

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

lib/theme/component_themes.dart

@@ -97,7 +97,7 @@ class ComponentThemes {
   static InputDecorationTheme inputDecorationTheme(ColorScheme colorScheme) {
     return InputDecorationTheme(
       filled: true,
-      fillColor: colorScheme.surfaceContainerHighest.withOpacity(0.5),
+      fillColor: colorScheme.surfaceContainerHighest.withValues(alpha: 0.5),
       contentPadding: EdgeInsets.symmetric(
         horizontal: AppSpacing.inputPadding,
         vertical: AppSpacing.md,
@@ -105,13 +105,13 @@ class ComponentThemes {
       border: OutlineInputBorder(
         borderRadius: AppBorders.circularSm,
         borderSide: BorderSide(
-          color: colorScheme.outline.withOpacity(0.3),
+          color: colorScheme.outline.withValues(alpha: 0.3),
         ),
       ),
       enabledBorder: OutlineInputBorder(
         borderRadius: AppBorders.circularSm,
         borderSide: BorderSide(
-          color: colorScheme.outline.withOpacity(0.3),
+          color: colorScheme.outline.withValues(alpha: 0.3),
           width: 1,
         ),
       ),
@@ -144,7 +144,7 @@ class ComponentThemes {
       hintStyle: TextStyle(
         fontFamily: 'Montserrat',
         fontWeight: FontWeight.w400,
-        color: colorScheme.onSurfaceVariant.withOpacity(0.6),
+        color: colorScheme.onSurfaceVariant.withValues(alpha: 0.6),
       ),
     );
   }
@@ -204,7 +204,7 @@ class ComponentThemes {
     return ChipThemeData(
       backgroundColor: colorScheme.surfaceContainerHighest,
       deleteIconColor: colorScheme.onSurfaceVariant,
-      disabledColor: colorScheme.surfaceContainerHighest.withOpacity(0.38),
+      disabledColor: colorScheme.surfaceContainerHighest.withValues(alpha: 0.38),
       padding: EdgeInsets.symmetric(
         horizontal: AppSpacing.sm,
         vertical: AppSpacing.xs,
@@ -255,7 +255,7 @@ class ComponentThemes {
       activeTrackColor: colorScheme.primary,
       inactiveTrackColor: colorScheme.surfaceContainerHighest,
       thumbColor: colorScheme.primary,
-      overlayColor: colorScheme.primary.withOpacity(0.12),
+      overlayColor: colorScheme.primary.withValues(alpha: 0.12),
       valueIndicatorColor: colorScheme.primary,
     );
   }

lib/theme/gradient_system.dart

@@ -75,7 +75,7 @@ class AppGradients {
       end: horizontal ? Alignment.centerRight : Alignment.bottomCenter,
       colors: [
         color,
-        color.withOpacity(0.8),
+        color.withValues(alpha: 0.8),
       ],
     );
   }
@@ -311,7 +311,7 @@ class AppGradients {
       begin: gradient.begin,
       end: gradient.end,
       colors: gradient.colors
-          .map((color) => color.withOpacity(opacity))
+          .map((color) => color.withValues(alpha: opacity))
           .toList(),
       stops: gradient.stops,
     );

lib/theme/size_system.dart

@@ -1,4 +1,3 @@
-import 'package:flutter/material.dart';
 
 /// Svrnty Size System
 /// Standard sizing constants for icons, buttons, containers, and other components

lib/theme/typography_system.dart

@@ -257,7 +257,7 @@ class AppTypography {
   ) {
     final color = baseStyle.color ?? Colors.black;
     return baseStyle.copyWith(
-      color: color.withOpacity(opacity),
+      color: color.withValues(alpha: opacity),
     );
   }