release.yml: set -e -x + explicit .deb presence check on builds

Without set -e, a failing dpkg-buildpackage inside 'make deb' was
silently swallowed by the Makefile's 'mv ... || true' pattern,
which matches any leftover amd64 .deb and exits 0. The build step
then succeeded without producing an arm64 .deb.

This adds:
- set -e -x at the start of each build step (fail on first error,
  trace all commands so the root cause is visible in logs)
- explicit ls + exit 1 check after make deb to confirm the
  expected .deb was actually produced

If arm64 cross-build still fails, we'll see exactly where now.

.forgejo/workflows/release.yml

@@ -222,21 +222,45 @@ jobs:
         env:
           POSTIT_RUNTIME: linux-x64
         run: |
+          set -e -x
           TAG=$(jq -r '.tag' "$STATE_FILE")
           cd /src/_src
           echo "→ Building amd64 for POSTIT_GIT_TAG=$TAG"
           make deb POSTIT_GIT_TAG="$TAG" POSTIT_RUNTIME=linux-x64
+          DEB_AMD64=$(ls postit_*${TAG}-1_amd64.deb 2>/dev/null || true)
+          if [[ -z "$DEB_AMD64" ]]; then
+            echo "::error::Build .deb amd64 did not produce postit_*${TAG}-1_amd64.deb"
+            ls -la
+            exit 1
+          fi
+          echo "✓ Built $DEB_AMD64"
+          set +x
 
       - name: Build .deb arm64
         env:
           POSTIT_RUNTIME: linux-arm64
         run: |
+          set -e -x
           TAG=$(jq -r '.tag' "$STATE_FILE")
           cd /src/_src
           echo "→ Building arm64 for POSTIT_GIT_TAG=$TAG"
           # Cross-RID .NET depuis un hôte amd64 : standard, pas
           # besoin de runner arm64 natif.
           make deb POSTIT_GIT_TAG="$TAG" POSTIT_RUNTIME=linux-arm64
+          # Verify the arm64 .deb was actually produced. Without
+          # this check, a silent dpkg-buildpackage failure would
+          # let the step exit 0 (the Makefile's mv || true matches
+          # any leftover amd64 .deb and exits successfully), and
+          # the failure would only surface in the next step.
+          DEB_ARM64=$(ls postit_*${TAG}-1_arm64.deb 2>/dev/null || true)
+          if [[ -z "$DEB_ARM64" ]]; then
+            echo "::error::Build .deb arm64 did not produce postit_*${TAG}-1_arm64.deb"
+            echo "Inspect the dpkg-buildpackage output above for the root cause."
+            ls -la
+            exit 1
+          fi
+          echo "✓ Built $DEB_ARM64"
+          set +x
 
       - name: Localiser les .deb produits
         run: |