feat: Inline title editing in DetailPanel — no more JS prompt

DetailPanel.tsx:
- Replaced window.prompt with native inline editing
- Click title text or 'Rename' button to enter edit mode
- Input field with lyria-accent border, focus ring, and placeholder
- Auto-focus + select-all on enter edit mode (useEffect)
- Enter to save, Escape to cancel, blur to save
- Title text has hover:bg-white/5 for visual feedback
- Non-editing title is clickable (cursor-pointer, title tooltip)
- Uses useState for edit mode and draft text, useRef for input focus

frontend/src/components/DetailPanel.tsx

@@ -1,4 +1,4 @@
-import { useRef } from 'react'
+import { useRef, useState, useEffect } from 'react'
 
 interface Clip {
   id: string
@@ -32,10 +32,40 @@ const modelName = (modelId: string) => {
 
 export default function DetailPanel({ clip, onClose, onRename, onDelete, onUploadArtwork, onRemoveArtwork }: Props) {
   const artworkInputRef = useRef<HTMLInputElement>(null)
-  const handleRename = () => {
-    const newTitle = window.prompt('Rename track:', clip.title || '')
-    if (newTitle !== null) {
-      onRename(clip.id, newTitle)
+  const [isEditingTitle, setIsEditingTitle] = useState(false)
+  const [editTitle, setEditTitle] = useState(clip.title || '')
+  const titleInputRef = useRef<HTMLInputElement>(null)
+
+  // Focus and select when entering edit mode
+  useEffect(() => {
+    if (isEditingTitle && titleInputRef.current) {
+      titleInputRef.current.focus()
+      titleInputRef.current.select()
+    }
+  }, [isEditingTitle])
+
+  const startEditing = () => {
+    setEditTitle(clip.title || '')
+    setIsEditingTitle(true)
+  }
+
+  const saveTitle = () => {
+    if (editTitle.trim() !== (clip.title || '')) {
+      onRename(clip.id, editTitle.trim())
+    }
+    setIsEditingTitle(false)
+  }
+
+  const cancelEditing = () => {
+    setEditTitle(clip.title || '')
+    setIsEditingTitle(false)
+  }
+
+  const handleTitleKeyDown = (e: React.KeyboardEvent) => {
+    if (e.key === 'Enter') {
+      saveTitle()
+    } else if (e.key === 'Escape') {
+      cancelEditing()
     }
   }
 
@@ -152,20 +182,38 @@ export default function DetailPanel({ clip, onClose, onRename, onDelete, onUploa
             </div>
           )}
 
-          {/* Title */}
+          {/* Title — inline editable */}
           <div>
             <div className="flex items-center justify-between mb-1">
               <label className="text-xs text-lyria-muted uppercase tracking-wider">Title</label>
-              <button
-                onClick={handleRename}
-                className="text-xs text-lyria-accent hover:text-lyria-accent/80 transition-colors"
-              >
-                Rename
-              </button>
+              {!isEditingTitle && (
+                <button
+                  onClick={startEditing}
+                  className="text-xs text-lyria-accent hover:text-lyria-accent/80 transition-colors"
+                >
+                  Rename
+                </button>
+              )}
             </div>
-            <p className="text-white text-lg font-medium">
-              {clip.title || <span className="text-lyria-muted italic">Untitled</span>}
-            </p>
+            {isEditingTitle ? (
+              <input
+                ref={titleInputRef}
+                type="text"
+                value={editTitle}
+                onChange={(e) => setEditTitle(e.target.value)}
+                onBlur={saveTitle}
+                onKeyDown={handleTitleKeyDown}
+                className="w-full bg-white/5 border border-lyria-accent/50 rounded-md px-3 py-2 text-white text-lg font-medium outline-none focus:border-lyria-accent focus:ring-1 focus:ring-lyria-accent/30 transition-all"
+                placeholder="Track title..."
+              />
+            ) : (
+              <p className="text-white text-lg font-medium px-3 py-2 -mx-3 rounded-md hover:bg-white/5 transition-colors cursor-pointer"
+                 onClick={startEditing}
+                 title="Click to rename"
+              >
+                {clip.title || <span className="text-lyria-muted italic">Untitled</span>}
+              </p>
+            )}
           </div>
 
           {/* Prompt */}