feat(05-01): redesign ImageUpload as hero area and move to top of forms

- Full-width 4:3 aspect ratio hero image area with rounded corners
- Placeholder state: gray background with ImagePlus icon and helper text
- Preview state: object-cover image with circular X remove button
- Upload state: semi-transparent spinner overlay
- Entire area clickable to upload/replace image
- Moved ImageUpload to first element in both ItemForm and CandidateForm
- Removed redundant "Image" label wrappers

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

src/client/components/CandidateForm.tsx

@@ -134,6 +134,14 @@ export function CandidateForm({
 
   return (
     <form onSubmit={handleSubmit} className="space-y-5">
+      {/* Image */}
+      <ImageUpload
+        value={form.imageFilename}
+        onChange={(filename) =>
+          setForm((f) => ({ ...f, imageFilename: filename }))
+        }
+      />
+
       {/* Name */}
       <div>
         <label
@@ -258,19 +266,6 @@ export function CandidateForm({
         )}
       </div>
 
-      {/* Image */}
-      <div>
-        <label className="block text-sm font-medium text-gray-700 mb-1">
-          Image
-        </label>
-        <ImageUpload
-          value={form.imageFilename}
-          onChange={(filename) =>
-            setForm((f) => ({ ...f, imageFilename: filename }))
-          }
-        />
-      </div>
-
       {/* Actions */}
       <div className="flex gap-3 pt-2">
         <button