List the files under a path by path, not by string prefix (closes #223)

FileRepository.ListByPrefix matched with SQL LIKE: a plain string
prefix that ignores ASCII case and treats _ and % as wildcards.
Restoring /home/u/doc also restored doc2, DOC and doc.txt.bak, and a
backup counted the files of a longer sibling path as deleted. It is
now ListUnderPath, which returns the file at the path and every file
whose path starts with the path plus a slash, compared exactly. A
trailing slash is ignored, so "/" still lists every file.

Three tests relied on string-prefix matching and now name a full path
or call ListAll.

ListIDsWithChunksNotInUploadedBlobs keeps its LIKE: it only adds file
IDs the scan never looks up.

Model: opus-5-5

TODO.md

@@ -22,6 +22,17 @@ the tag exists and is exercised; what is left is merging `next` to
 
 # Completed Steps
 
+- 2026-10-06: Made a restore path argument select only that path and
+  what is beneath it
+  ([issue #223](https://git.eeqj.de/sneak/vaultik/issues/223)). The
+  lookup matched with SQL `LIKE`, so `/home/u/doc` also restored
+  `doc2`, `DOC` and `doc.txt.bak`, and a `_` or `%` in the path acted
+  as a wildcard. A backup used the same lookup to load the known files
+  of each configured path, so files of a longer sibling path were
+  counted as deleted. `FileRepository.ListUnderPath`, which replaces
+  `ListByPrefix`, returns the file at the path and every file whose
+  path starts with the path plus `/`, compared case-sensitively.
+
 - 2026-10-06: Made restore return an error instead of panicking on a
   malformed snapshot database
   ([issue #231](https://git.eeqj.de/sneak/vaultik/issues/231)). A chunk