Refresh before backup-metadata and the thumbnail helpers answer (closes #100)

backup-metadata, helper list-missing-thumbnails and helper
fix-missing-thumbnails now await lib.fresh() before reading the library,
as collections, files, get and get-thumb already do. A file added since
the cache was written is included, and a failed refresh is thrown, so
the CLI prints one line and exits 1 instead of answering from a stale
or empty cache. The README lists them among the commands that refresh
first.

Model: opus-5-5

TODO.md

@@ -18,6 +18,13 @@ Tag v1.0.0.
 
 # Completed Steps
 
+- 2026-09-23: `backup-metadata`, `helper list-missing-thumbnails` and
+  `helper fix-missing-thumbnails` refresh before they answer (issue 100). Each
+  awaits `lib.fresh()` before reading, so a file added since the cache was
+  written is included, and a failed refresh prints one line and exits 1 instead
+  of answering from a stale or empty cache. The README lists them among the
+  commands that refresh first.
+
 - 2026-09-23: CLI errors print a message instead of a stack trace (issue 102).
   An error a command throws is printed as one `quak: MESSAGE` line on stderr and
   the CLI exits 1 once output has drained. The wrapper that does this moved from