rclone-backup: fall back to raw copy for non-SQLite DBs

filebrowser's database.db is BoltDB, not SQLite, so sqlite .backup left a
0-byte snapshot. Try .backup and fall back to cp when it isn't SQLite (or
is locked), so every DB gets a usable snapshot.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

modules/fileserver.nix

@@ -317,8 +317,13 @@
           /data/daten/DJing/Data/MusicLibrary.db; do
           [ -f "$db" ] || continue
           out="$SNAP/$(echo "$db" | sed 's#^/data/##; s#/#_#g')"
-          ${pkgs.sqlite}/bin/sqlite3 "$db" ".timeout 15000" ".backup '$out'" \
-            || echo "WARN: snapshot of $db failed" >&2
+          # Echtes SQLite -> konsistentes .backup. Andernfalls (filebrowser
+          # nutzt z.B. BoltDB) oder bei Sperre auf eine Rohkopie zurückfallen.
+          if ${pkgs.sqlite}/bin/sqlite3 "$db" ".timeout 15000" ".backup '$out'" 2>/dev/null && [ -s "$out" ]; then
+            :
+          else
+            cp -f "$db" "$out" || echo "WARN: snapshot of $db failed" >&2
+          fi
         done
 
         ${pkgs.rclone}/bin/rclone sync /data gdrive:backup-daten \