feat(08-02): migrate UI primitives to semantic MD3 token classes

- BackendCard: border-blue-600/bg-blue-50 -> border-primary/bg-primary/10, border-gray-200/bg-white -> border-outline/bg-surface-container, text-gray-900 -> text-on-surface, text-gray-500 -> text-on-surface-container/70
- FieldRenderer: text-gray-700 -> text-on-surface-container, text-red-500 -> text-error, text-blue-500/700 -> text-primary, bg-blue-50/border-blue-200 -> bg-primary/10/border-primary/30, border-red-500 -> border-error, focus:ring-red-300 -> focus:ring-error/50, border-gray-300 -> border-outline, focus:ring-blue-300 -> focus:ring-primary/50, text-gray-500 -> text-on-surface-container/70, text-red-600 -> text-error
- PasswordField: same mapping as FieldRenderer + text-gray-400/hover:text-gray-700 -> text-on-surface-container/50 hover:text-on-surface-container

src/components/ui/BackendCard.tsx

@@ -16,13 +16,13 @@ export function BackendCard({ name, description, selected = false, onClick, ...r
       className={[
         'flex flex-col items-start gap-1 rounded-lg border-2 p-4 text-left transition-colors',
         selected
-          ? 'border-blue-600 bg-blue-50'
+          ? 'border-primary bg-primary/10'
-          : 'border-gray-200 bg-white hover:border-blue-400 hover:bg-gray-50',
+          : 'border-outline bg-surface-container hover:border-primary hover:bg-surface',
       ].join(' ')}
       {...rest}
     >
-      <span className="font-semibold text-gray-900">{name}</span>
+      <span className="font-semibold text-on-surface">{name}</span>
-      <span className="text-sm text-gray-500">{description}</span>
+      <span className="text-sm text-on-surface-container/70">{description}</span>
     </button>
   );
 }

src/components/ui/FieldRenderer.tsx

@@ -41,23 +41,23 @@ export function FieldRenderer({ field, register, error }: FieldRendererProps) {
     return (
       <div className="flex flex-col gap-1">
         <div className="flex items-center gap-1">
-          <label htmlFor={field.key} className="text-sm font-medium text-gray-700">
+          <label htmlFor={field.key} className="text-sm font-medium text-on-surface-container">
             {field.label}
-            {field.required && <span className="ml-1 text-red-500">*</span>}
+            {field.required && <span className="ml-1 text-error">*</span>}
           </label>
           {field.tooltipText && (
             <button
               type="button"
               onClick={() => setShowTooltip(v => !v)}
               aria-label={`More info about ${field.label}`}
-              className="text-blue-500 hover:text-blue-700 text-xs leading-none"
+              className="text-primary hover:text-primary text-xs leading-none"
             >
               ⓘ
             </button>
           )}
         </div>
         {field.tooltipText && showTooltip && (
-          <p className="text-xs text-blue-700 bg-blue-50 border border-blue-200 rounded px-2 py-1.5 mt-1">
+          <p className="text-xs text-primary bg-primary/10 border border-primary/30 rounded px-2 py-1.5 mt-1">
             {field.tooltipText}
           </p>
         )}
@@ -65,7 +65,7 @@ export function FieldRenderer({ field, register, error }: FieldRendererProps) {
           id={field.key}
           className={[
             'w-full rounded-md border px-3 py-2 text-sm focus:outline-none focus:ring-2',
-            error ? 'border-red-500 focus:ring-red-300' : 'border-gray-300 focus:ring-blue-300',
+            error ? 'border-error focus:ring-error/50' : 'border-outline focus:ring-primary/50',
           ].join(' ')}
           {...register(field.key)}
         >
@@ -73,8 +73,8 @@ export function FieldRenderer({ field, register, error }: FieldRendererProps) {
             <option key={opt.value} value={opt.value}>{opt.label}</option>
           ))}
         </select>
-        {field.helpText && !error && <p className="text-xs text-gray-500">{field.helpText}</p>}
+        {field.helpText && !error && <p className="text-xs text-on-surface-container/70">{field.helpText}</p>}
-        {error && <p className="text-xs text-red-600">{error.message}</p>}
+        {error && <p className="text-xs text-error">{error.message}</p>}
       </div>
     );
   }
@@ -85,13 +85,13 @@ export function FieldRenderer({ field, register, error }: FieldRendererProps) {
       <div className="flex items-center gap-1">
         <label htmlFor={field.key} className="text-sm font-medium text-gray-700">
           {field.label}
-          {field.required && <span className="ml-1 text-red-500">*</span>}
+          {field.required && <span className="ml-1 text-error">*</span>}
         </label>
         {field.tooltipText && (
           <button
             type="button"
             onClick={() => setShowTooltip(v => !v)}
-            className="text-blue-500 hover:text-blue-700 text-xs leading-none"
+            className="text-primary hover:text-primary text-xs leading-none"
           >
             <span className="sr-only">More info about {field.label}</span>
             <span aria-hidden="true">ⓘ</span>
@@ -109,12 +109,12 @@ export function FieldRenderer({ field, register, error }: FieldRendererProps) {
         placeholder={field.placeholder}
         className={[
           'w-full rounded-md border px-3 py-2 text-sm focus:outline-none focus:ring-2',
-          error ? 'border-red-500 focus:ring-red-300' : 'border-gray-300 focus:ring-blue-300',
+          error ? 'border-error focus:ring-error/50' : 'border-outline focus:ring-primary/50',
         ].join(' ')}
         {...register(field.key)}
       />
-      {field.helpText && !error && <p className="text-xs text-gray-500">{field.helpText}</p>}
+      {field.helpText && !error && <p className="text-xs text-on-surface-container/70">{field.helpText}</p>}
-      {error && <p className="text-xs text-red-600">{error.message}</p>}
+      {error && <p className="text-xs text-error">{error.message}</p>}
     </div>
   );
 }

src/components/ui/PasswordField.tsx

@@ -17,14 +17,14 @@ export function PasswordField({ id, label, error, registration, placeholder, hel
   return (
     <div className="flex flex-col gap-1">
       <div className="flex items-center gap-1">
-        <label htmlFor={id} className="text-sm font-medium text-gray-700">
+        <label htmlFor={id} className="text-sm font-medium text-on-surface-container">
           {label}
         </label>
         {tooltipText && (
           <button
             type="button"
             onClick={() => setShowTooltip(v => !v)}
-            className="text-blue-500 hover:text-blue-700 text-xs leading-none"
+            className="text-primary hover:text-primary text-xs leading-none"
           >
             <span className="sr-only">More info about {label}</span>
             <span aria-hidden="true">ⓘ</span>
@@ -32,7 +32,7 @@ export function PasswordField({ id, label, error, registration, placeholder, hel
         )}
       </div>
       {tooltipText && showTooltip && (
-        <p className="text-xs text-blue-700 bg-blue-50 border border-blue-200 rounded px-2 py-1.5 mt-1">
+        <p className="text-xs text-primary bg-primary/10 border border-primary/30 rounded px-2 py-1.5 mt-1">
           {tooltipText}
         </p>
       )}
@@ -43,7 +43,7 @@ export function PasswordField({ id, label, error, registration, placeholder, hel
           placeholder={placeholder}
           className={[
             'w-full rounded-md border px-3 py-2 pr-10 text-sm focus:outline-none focus:ring-2',
-            error ? 'border-red-500 focus:ring-red-300' : 'border-gray-300 focus:ring-blue-300',
+            error ? 'border-error focus:ring-error/50' : 'border-outline focus:ring-primary/50',
           ].join(' ')}
           {...registration}
         />
@@ -51,13 +51,13 @@ export function PasswordField({ id, label, error, registration, placeholder, hel
           type="button"
           onClick={() => setShow(v => !v)}
           aria-label={show ? 'Hide' : 'Show'}
-          className="absolute right-2 top-1/2 -translate-y-1/2 text-gray-400 hover:text-gray-700"
+          className="absolute right-2 top-1/2 -translate-y-1/2 text-on-surface-container/50 hover:text-on-surface-container"
         >
           {show ? 'Hide' : 'Show'}
         </button>
       </div>
-      {helpText && !error && <p className="text-xs text-gray-500">{helpText}</p>}
+      {helpText && !error && <p className="text-xs text-on-surface-container/70">{helpText}</p>}
-      {error && <p className="text-xs text-red-600">{error.message}</p>}
+      {error && <p className="text-xs text-error">{error.message}</p>}
     </div>
   );
 }