fix: make image read-only for reference items, rename delete to remove

- Reference items show catalog image as read-only in edit mode (no upload)
- "Delete" button renamed to "Remove from Collection" for reference items

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

src/client/routes/items/$itemId.tsx

@@ -198,7 +198,7 @@ function ItemDetail() {
 							onClick={handleDelete}
 							className="px-3 py-1.5 text-sm text-red-400 hover:text-red-600 hover:bg-red-50 rounded-lg transition-colors"
 						>
-							Delete
+							{isReference ? "Remove from Collection" : "Delete"}
 						</button>
 						<button
 							type="button"
@@ -231,7 +231,7 @@ function ItemDetail() {
 			</div>
 
 			{/* Hero image */}
-			{isEditing ? (
+			{isEditing && !isReference ? (
 				<div className="mb-6">
 					<ImageUpload
 						value={form.imageFilename}