Merge assets-panel empty state into one dropzone

The Assets panel used to show a small always-visible dropzone plus a
separate italic "No assets uploaded yet" line stacked underneath it
when there were no assets -- two redundant messages for one state.
Replace both with a single tall dropzone (icon + "Drag images here or
click to upload") that also opens the file picker on click; it
collapses back to the original slim "Drop files here to upload" bar
once assets exist. Upload/drag-drop behavior is unchanged.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

craft/src/panels/left/AssetsPanel.tsx

@@ -107,23 +107,41 @@ export const AssetsPanel: React.FC = () => {
         {loading ? 'Uploading...' : 'Upload File'}
       </button>
 
-      {/* Drop zone */}
+      {/* Drop zone -- a single element that doubles as the empty state.
+          Previously this was a small always-visible dropzone PLUS a
+          separate italic "No assets uploaded yet" line stacked underneath
+          it when empty; merged into one tall dropzone (icon + copy,
+          click-or-drag) so the empty state isn't two redundant messages.
+          Once assets exist it collapses back to a slim persistent drop
+          target above the grid. */}
       <div
         onDrop={handleDrop}
         onDragOver={handleDragOver}
         onDragLeave={handleDragLeave}
+        onClick={assets.length === 0 ? () => fileInputRef.current?.click() : undefined}
+        role={assets.length === 0 ? 'button' : undefined}
+        tabIndex={assets.length === 0 ? 0 : undefined}
         style={{
-          padding: 20,
+          display: 'flex',
+          flexDirection: 'column',
+          alignItems: 'center',
+          justifyContent: 'center',
+          gap: 8,
+          padding: assets.length === 0 ? '36px 20px' : 16,
           border: `2px dashed ${isDragOver ? 'var(--color-accent)' : 'var(--color-border)'}`,
           borderRadius: 'var(--radius-md)',
           background: isDragOver ? 'var(--color-accent-subtle)' : 'transparent',
           textAlign: 'center',
           color: isDragOver ? 'var(--color-accent)' : 'var(--color-text-dim)',
           fontSize: 11,
+          cursor: assets.length === 0 ? 'pointer' : 'default',
           transition: 'all var(--transition-fast)',
         }}
       >
-        Drop files here to upload
+        {assets.length === 0 && (
+          <i className="fa fa-cloud-upload" aria-hidden style={{ fontSize: 28, opacity: 0.5 }} />
+        )}
+        {assets.length === 0 ? 'Drag images here or click to upload' : 'Drop files here to upload'}
       </div>
 
       {/* Error message */}
@@ -143,20 +161,6 @@ export const AssetsPanel: React.FC = () => {
       )}
 
       {/* Asset grid */}
-      {assets.length === 0 && !loading && (
-        <div
-          style={{
-            textAlign: 'center',
-            padding: 20,
-            color: 'var(--color-text-dim)',
-            fontSize: 12,
-            fontStyle: 'italic',
-          }}
-        >
-          No assets uploaded yet
-        </div>
-      )}
-
       <div
         style={{
           display: 'grid',