fix(flatpak): GPG-sign repo summaries during build and deploy

Unsigned summary updates left stale summary.sig files on the server,
causing BAD signature errors for clients. Sign exports and summaries
with the BearWave repo key and require .sig files before deploy.

scripts/deploy-flatpak.sh

@@ -11,6 +11,11 @@ if [[ ! -d flatpak_repo/objects ]]; then
   exit 1
 fi
 
+if [[ ! -f flatpak_repo/summary.sig || ! -f flatpak_repo/summary.idx.sig ]]; then
+  echo "Missing summary.sig files. Run scripts/build-flatpak.sh with GPG signing first." >&2
+  exit 1
+fi
+
 rsync -avz \
   -e 'ssh -o RemoteCommand=none -o RequestTTY=no' \
   --no-group --no-owner \