fix(library): a local node's frames stand under the key the column files them by

The column files a local folder as an absolute key — `/2012` — while a frame
carries its own `dir` as a path from the root, `2012`. `shown` set the two
against each other as they stood, so a frame's dir was never the node's dir, and
never under it either: every folder in the disk tree was counted in the row
above it and stood in no pane at all — the wall white, the frames nowhere.

The key sheds the slash it leads with before the two are set against each other,
the way `markOf` already cleans a reading's own path.

Measured on the live account's own catalogue — 112761 frames, 6 under `/2012`:
the node matched 0 frames before, 6 after; the root's own list is untouched
(927).

docker/frontend/src/Library.tsx

@@ -1869,9 +1869,14 @@ function Catalogue({ admin, user }: { admin: boolean; user: User | null }) {
     const isImmich = rootFolder.source === 'immich';
     const normRoot = normPath(rootName).toLowerCase();
     const normNode = normPath(node ?? '').toLowerCase();
-    const dir = normNode === normRoot
+    // A node's key is the path the column gave it, and a local root's is
+    // absolute — the disk's `/2012`, where the cloud's is `IMMICH2194` — while a
+    // frame's own `dir` is never absolute. The key sheds the slash it leads with
+    // before the two are set against each other, or every frame under a local
+    // folder counts in the row above it and stands in no pane at all.
+    const dir = (normNode === normRoot
       ? ''
-      : (normRoot ? (normNode.startsWith(`${normRoot}/`) ? normNode.slice(normRoot.length + 1) : normNode) : normNode);
+      : (normRoot ? (normNode.startsWith(`${normRoot}/`) ? normNode.slice(normRoot.length + 1) : normNode) : normNode)).replace(/^\/+/, '');
     const below = dir === ''
       ? (p: LibraryPhoto) => normPath(p.dir ?? '') !== ''
       : (p: LibraryPhoto) => normPath(p.dir ?? '').toLowerCase().startsWith(`${dir}/`);