fix: use CSS variables for dark mode support in settings page

Replace hard-coded colors with CSS variables from the theme system to
properly support both light and dark modes. Also add proper input
styling and strong tag emphasis colors.

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

src/frontend/src/routes/settings/+page.svelte

@@ -440,40 +440,46 @@
 
   .header h1 {
     margin: 0;
-    color: #333;
+    color: var(--text-primary);
   }
 
   .back-button {
     padding: 0.5rem 1rem;
-    background-color: #6c757d;
-    color: white;
+    background-color: var(--color-secondary);
+    color: var(--text-inverted);
     text-decoration: none;
-    border-radius: 4px;
+    border-radius: var(--border-radius);
     font-size: 0.9rem;
     font-weight: 500;
     transition: background-color 0.2s;
   }
 
   .back-button:hover {
-    background-color: #5a6268;
+    background-color: var(--color-secondary-hover);
   }
 
   .user-info {
-    background: #f8f9fa;
+    background: var(--bg-secondary);
     padding: 1.5rem;
-    border-radius: 8px;
+    border-radius: var(--border-radius-lg);
     margin-bottom: 2rem;
   }
 
   .user-info h2 {
     margin: 0 0 1rem 0;
     font-size: 1.25rem;
-    color: #333;
+    color: var(--text-primary);
   }
 
   .user-info p {
     margin: 0.5rem 0;
-    color: #666;
+    color: var(--text-secondary);
+  }
+
+  .user-info :global(strong),
+  .settings-form :global(strong),
+  .next-sync-info :global(strong) {
+    color: var(--text-primary);
   }
 
   .settings-section {
@@ -483,44 +489,44 @@
   .settings-section h2 {
     margin: 0 0 0.5rem 0;
     font-size: 1.25rem;
-    color: #333;
+    color: var(--text-primary);
   }
 
   .help-text {
-    color: #666;
+    color: var(--text-secondary);
     margin-bottom: 1.5rem;
     line-height: 1.6;
   }
 
   .alert {
     padding: 1rem;
-    border-radius: 4px;
+    border-radius: var(--border-radius);
     margin-bottom: 1.5rem;
   }
 
   .alert-info {
-    background-color: #d1ecf1;
-    border: 1px solid #bee5eb;
-    color: #0c5460;
+    background-color: var(--color-info-bg);
+    border: 1px solid var(--color-info);
+    color: var(--color-info-text);
   }
 
   .alert-error {
-    background-color: #f8d7da;
-    border: 1px solid #f5c6cb;
-    color: #721c24;
+    background-color: var(--color-error-bg);
+    border: 1px solid var(--color-error);
+    color: var(--color-error-text);
   }
 
   .alert-success {
-    background-color: #d4edda;
-    border: 1px solid #c3e6cb;
-    color: #155724;
+    background-color: var(--color-success-bg);
+    border: 1px solid var(--color-success);
+    color: var(--color-success);
   }
 
   .settings-form {
-    background: white;
+    background: var(--bg-card);
     padding: 2rem;
-    border: 1px solid #e0e0e0;
-    border-radius: 8px;
+    border: 1px solid var(--border-color);
+    border-radius: var(--border-radius-lg);
     margin-bottom: 2rem;
   }
 
@@ -532,34 +538,36 @@
     display: block;
     margin-bottom: 0.5rem;
     font-weight: 500;
-    color: #333;
+    color: var(--text-primary);
   }
 
   .form-group input {
     width: 100%;
     padding: 0.75rem;
-    border: 1px solid #ddd;
-    border-radius: 4px;
+    border: 1px solid var(--border-color);
+    border-radius: var(--border-radius);
     font-size: 1rem;
+    background: var(--bg-input);
+    color: var(--text-primary);
     box-sizing: border-box;
   }
 
   .form-group input:focus {
     outline: none;
-    border-color: #4a90e2;
-    box-shadow: 0 0 0 3px rgba(74, 144, 226, 0.1);
+    border-color: var(--color-primary);
+    box-shadow: var(--focus-ring);
   }
 
   .hint {
     font-size: 0.875rem;
-    color: #666;
+    color: var(--text-secondary);
     margin-top: 0.5rem;
   }
 
   .btn {
     padding: 0.75rem 1.5rem;
     border: none;
-    border-radius: 4px;
+    border-radius: var(--border-radius);
     font-size: 1rem;
     font-weight: 500;
     cursor: pointer;
@@ -567,12 +575,12 @@
   }
 
   .btn-primary {
-    background-color: #4a90e2;
-    color: white;
+    background-color: var(--color-primary);
+    color: var(--text-inverted);
   }
 
   .btn-primary:hover:not(:disabled) {
-    background-color: #357abd;
+    background-color: var(--color-primary-hover);
   }
 
   .btn-primary:disabled {
@@ -581,34 +589,34 @@
   }
 
   .btn-secondary {
-    background-color: #6c757d;
-    color: white;
+    background-color: var(--color-secondary);
+    color: var(--text-inverted);
   }
 
   .btn-secondary:hover {
-    background-color: #5a6268;
+    background-color: var(--color-secondary-hover);
   }
 
   .info-box {
-    background: #e8f4fd;
-    border-left: 4px solid #4a90e2;
+    background: var(--color-info-bg);
+    border-left: 4px solid var(--color-primary);
     padding: 1.5rem;
-    border-radius: 4px;
+    border-radius: var(--border-radius);
   }
 
   .info-box h3 {
     margin: 0 0 1rem 0;
-    color: #333;
+    color: var(--text-primary);
   }
 
   .info-box p {
     margin: 0.5rem 0;
-    color: #666;
+    color: var(--text-secondary);
     line-height: 1.6;
   }
 
   .info-box a {
-    color: #4a90e2;
+    color: var(--text-link);
     text-decoration: none;
   }
 
@@ -634,6 +642,7 @@
     gap: 0.5rem;
     font-weight: 500;
     cursor: pointer;
+    color: var(--text-primary);
   }
 
   .checkbox-group input[type="checkbox"] {
@@ -649,18 +658,18 @@
 
   .divider {
     border: none;
-    border-top: 1px solid #e0e0e0;
+    border-top: 1px solid var(--border-color);
     margin: 2rem 0;
   }
 
   .next-sync-info {
     padding: 0.75rem 1rem;
-    background-color: #e3f2fd;
-    border-left: 4px solid #4a90e2;
-    border-radius: 4px;
+    background-color: var(--color-info-bg);
+    border-left: 4px solid var(--color-primary);
+    border-radius: var(--border-radius);
     margin-top: 1rem;
     font-size: 0.9rem;
-    color: #333;
+    color: var(--text-primary);
   }
 
   @media (max-width: 640px) {