Count a file as deleted only if the previous snapshot of its name had it (closes #304)

A backup counted as deleted every file in the local index under the
source path that the walk did not find. That took in files the
snapshot excludes but another snapshot backs up, and files removed long
ago, which every later backup, and the first backup of another name
over the same path, reported as deleted again.

The backup now looks up the most recent completed snapshot of the same
name and counts only the files it lists that the walk did not find and
that are not excluded.

The snapshots row stores no deleted figure; only the backup's output
changes.

Model: opus-5-5

TODO.md

@@ -22,6 +22,18 @@ the tag exists and is exercised; what is left is merging `next` to
 
 # Completed Steps
 
+- 2026-10-13: Counted a file as deleted only when the previous snapshot
+  of the same name had it
+  ([issue #304](https://git.eeqj.de/sneak/vaultik/issues/304)). The
+  deleted figure of a backup counted every file in the local index under
+  the source path that the walk did not find. That took in files the
+  snapshot excludes but another snapshot backs up, and files deleted
+  long ago, which every later backup, and the first backup of another
+  name over the same path, reported as deleted again. A file is now
+  counted only when the previous completed snapshot of the same name
+  lists it and the walk did not find it, and an excluded file is never
+  counted.
+
 - 2026-10-13: Made `snapshot remove` fail for a snapshot that does not
   exist ([issue #293](https://git.eeqj.de/sneak/vaultik/issues/293)).
   The command never checked the ID: it reported the snapshot removed