ui(duplicates): show grandparent + parent in path strip

When two duplicates live in folders with the same parent name (e.g.
matching '2023' subfolders under different archives), showing only
the parent gave both thumbnails the same label. Walk one level up:
the path strip now renders '…/<grandparent>/<parent>' so the user
can always tell two copies apart at a glance. Filename still
surfaces via the title tooltip.

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

frontend/src/components/duplicates/DuplicatesView.tsx

@@ -515,20 +515,25 @@ function formatBytes(n: number): string {
 }
 
 /** Short label for the bottom path strip on a duplicate thumbnail.
- *  Goal: tell two copies-with-the-same-filename apart at a glance, so
- *  we want the parent folder name — that's almost always the
- *  discriminator (different shoots, different years, different
- *  upload sources). When the parent folder is unhelpful (e.g. the
- *  filename is itself sitting at the root) we fall back to the file
- *  basename. Long folder names get text-overflow-ellipsis'd by the
- *  enclosing strip's `truncate`. */
+ *  Goal: tell two copies-with-the-same-filename apart at a glance.
+ *  Shows the last two folders ("…/<grandparent>/<parent>") so the
+ *  discriminator is visible even when both copies live under the
+ *  same parent name (e.g. matching `2023` subfolders under different
+ *  archives). The leading "…/" is always present when there's any
+ *  truncated prefix; the enclosing strip's `truncate` handles any
+ *  excess width. */
 function duplicatePathLabel(filepath: string): string {
   if (!filepath) return ''
   const parts = filepath.split('/').filter(Boolean)
   if (parts.length === 0) return filepath
-  if (parts.length === 1) return parts[0]
-  // The second-to-last segment IS the parent directory.
-  return parts[parts.length - 2]
+  // Strip the filename (last segment); only the directory chain
+  // discriminates between copies with matching basenames.
+  const folders = parts.slice(0, -1)
+  if (folders.length === 0) return parts[0]
+  if (folders.length === 1) return `…/${folders[0]}`
+  const parent = folders[folders.length - 1]
+  const grandparent = folders[folders.length - 2]
+  return `…/${grandparent}/${parent}`
 }
 
 /** Adapt a DuplicateGroupMember (the slim API shape) to a Photo, which