fix(student-attempt): drop duplicate save indicator in header card

Both the header card and the sticky floating indicator rendered a
SaveIndicator at the top of the page, so users saw "Not saved yet" twice
side by side. Keep only the sticky one — it stays visible when scrolled,
which is what the user needs.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

Author: WangYuTengg

src/client/features/student-assignment/components/AssignmentHeader.tsx

@@ -156,31 +156,20 @@ export function AssignmentHeader({
         </div>
       )}
       <div className="bg-white shadow rounded-lg p-6">
-        <div className="flex justify-between items-start">
-          <div className="flex-1">
-            <h1 className="text-2xl font-bold text-gray-900">{assignment.title}</h1>
-            {assignment.description && <p className="mt-2 text-gray-600">{assignment.description}</p>}
-            {dueDate && <p className="mt-2 text-sm text-gray-500">Due: {dueDate.toLocaleString()}</p>}
-            <div className="mt-3 flex flex-wrap items-center gap-2">
-              <span className="text-sm font-medium text-gray-700">
-                {assignment.questionCount} question{assignment.questionCount === 1 ? '' : 's'}
+        <div className="flex-1">
+          <h1 className="text-2xl font-bold text-gray-900">{assignment.title}</h1>
+          {assignment.description && <p className="mt-2 text-gray-600">{assignment.description}</p>}
+          {dueDate && <p className="mt-2 text-sm text-gray-500">Due: {dueDate.toLocaleString()}</p>}
+          <div className="mt-3 flex flex-wrap items-center gap-2">
+            <span className="text-sm font-medium text-gray-700">
+              {assignment.questionCount} question{assignment.questionCount === 1 ? '' : 's'}
+            </span>
+            {visibleQuestionTypes.map((type) => (
+              <span key={type} className={getQuestionTypeBadgeClasses(type)}>
+                {assignment.questionTypeCounts[type]} {QUESTION_TYPE_LABELS[type]}
               </span>
-              {visibleQuestionTypes.map((type) => (
-                <span key={type} className={getQuestionTypeBadgeClasses(type)}>
-                  {assignment.questionTypeCounts[type]} {QUESTION_TYPE_LABELS[type]}
-                </span>
-              ))}
-            </div>
+            ))}
           </div>
-          {!submitted && (
-            <div className="shrink-0">
-              <SaveIndicator
-                status={saveStatus}
-                lastSaved={lastSaved ?? null}
-                onRetry={onRetrySave}
-              />
-            </div>
-          )}
         </div>
         {isPastDue && (
           <div className="mt-4 rounded-md bg-yellow-50 p-4">