Add milliseconds to photo filenames to prevent overwrites

Filenames now include milliseconds (e.g. kamaji_20260207_143022347.jpg)
so rapid consecutive captures don't produce identical names and
overwrite each other on Nextcloud.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

app/templates/capture.html

@@ -551,7 +551,8 @@ async function savePhoto(jpegBlob) {
         String(now.getDate()).padStart(2, '0') + '_' +
         String(now.getHours()).padStart(2, '0') +
         String(now.getMinutes()).padStart(2, '0') +
-        String(now.getSeconds()).padStart(2, '0');
+        String(now.getSeconds()).padStart(2, '0') +
+        String(now.getMilliseconds()).padStart(3, '0');
     const filename = currentUsername + '_' + timestamp + '.jpg';
     const targetPath = localStorage.getItem('nextsnap_upload_path') || '/';