fix: never descend into NAS metadata directories when indexing

The archive root was filtered by prefix, but the recursive walk below it was
not, so anything inside a profile directory got indexed. NAS filesystems put
sidecar metadata *inside* every folder rather than only at the share root:
Synology writes @eaDir (thumbnails and indexing data), #recycle holds
deletions, .sync is Resilio state. On the live share those account for 12,516
of 123,023 files.

None currently sit inside a profile directory, so nothing was miscounted yet —
but the moment that share gets indexed for Photos, every generated thumbnail
would be counted as archive media and stat'd one by one over the network, which
is the cost the index exists to avoid.

One isSystemDirectory rule now applies at every level, and the root listing uses
it too instead of keeping a second copy of the pattern.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_011uBWhwV3wFQ5MBCcMHHem7

package.json

@@ -1,7 +1,7 @@
 {
   "name": "instaarchive-viewer",
   "private": true,
-  "version": "1.5.0",
+  "version": "1.5.1",
   "type": "module",
   "scripts": {
     "dev": "vite --port=3000 --host=0.0.0.0",