fix: run full apt update in migration script to avoid false failure

The limited-scope apt-get update didn't flush the full apt cache, causing
apt-cache policy to miss the new GitHub Pages source on nodes that had a
beta build installed from the testing channel (pve02-hq: 3.0.0~beta).
Full apt update ensures the cache is consistent before the verification check.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

scripts/migrate-repo-to-github-pages.sh

@@ -117,9 +117,7 @@ cat "$SOURCES_FILE"
 # ── apt update ───────────────────────────────────────────────────────────────
 echo ""
 echo "==> Running apt update..."
-apt-get update -o Dir::Etc::sourcelist="$SOURCES_FILE" \
-               -o Dir::Etc::sourceparts="-" \
-               -o APT::Get::List-Cleanup="0" 2>&1 \
+apt-get update 2>&1 \
   | grep -E "^(Get|Hit|Err|Fetched|W:|E:)" || true
 
 # Confirm the package is visible from the new repo