nfs-mirror: append transferred files to offsite-sync manifest

Step 1 of offsite-sync-backup is incremental on non-monthly days,
driven by /mnt/backup/.changed-files which only daily-backup wrote
to. nfs-mirror's writes were therefore invisible to Step 1 until the
next monthly --delete pass — which would *also* wipe data
pre-positioned on Synology pve-backup/ (e.g. the in-place btrfs
rename we just did to relocate ~160G of NFS subtrees from
/Backup/Viki/nfs/<svc>/ to /Backup/Viki/pve-backup/<svc>/).

Fix: snapshot a timestamp before rsync, then after rsync use
`find -newer $STAMP -type f -printf '%P\n'` to enumerate every file
nfs-mirror created/modified and append to the manifest. Paths are
relative to /mnt/backup/ (matches Step 1 --files-from expectation).
State files are excluded.

The current in-flight first run started before this patch was
deployed, so its writes won't auto-populate the manifest — a one-off
manual backfill will be done after it completes.

stacks/recruiter-responder/terragrunt.hcl

@@ -19,5 +19,5 @@ dependency "external-secrets" {
 
 inputs = {
   # Override per-deploy in CI / commit.
-  image_tag = "83ffd9fa"
+  image_tag = "2162e09d"
 }