fix(ci): properly delete nightly builds older than 3 days (#217)

The previous cleanup logic sorted releases by column 3 which contained
relative dates like '3 days ago' as text. This doesn't work reliably
for sorting because '3 days ago' and '4 days ago' are compared as
strings, not dates.

This fix:
- Uses gh release list --json to get actual ISO 8601 creation timestamps
- Calculates a proper cutoff date (3 days ago in seconds since epoch)
- Parses and compares actual timestamps
- Only deletes releases that are truly older than 3 days

Fixes the nightly build retention policy.

.github/workflows/nightly.yml

@@ -84,16 +84,25 @@ jobs:
         env:
           GITHUB_TOKEN: ${{ secrets.GITHUB_TOKEN }}
         run: |
-          # Get list of nightly releases (tagged with nightly-YYYY-MM-DD), sorted by date descending
-          # Keep only the 3 most recent, delete the rest
-          gh release list --repo ${{ github.repository }} --limit 100 | \
-            grep "nightly-" | \
-            sort -t$'\t' -k3 -r | \
-            tail -n +4 | \
-            while IFS=$'\t' read -r tag name date; do
-              echo "Deleting old nightly release: $tag"
-              gh release delete "$tag" --yes --repo ${{ github.repository }} 2>/dev/null || true
-              git push origin :refs/tags/"$tag" 2>/dev/null || true
+          # Calculate the cutoff date (3 days ago) in seconds since epoch
+          CUTOFF_DATE=$(date -d '3 days ago' +%s)
+          echo "Cutoff date: $(date -d @$CUTOFF_DATE -u +"%Y-%m-%d %H:%M:%S UTC") (3 days ago)"
+
+          # Get nightly releases with their actual creation timestamps using JSON output
+          # Filter for releases older than 3 days and delete them
+          gh release list --repo ${{ github.repository }} --json tagName,createdAt --limit 100 | \
+            jq -r '.[] | select(.tagName | startswith("nightly-")) | [.tagName, .createdAt] | @tsv' | \
+            while IFS=$'\t' read -r tag created_at; do
+              # Parse the ISO 8601 date to seconds since epoch
+              RELEASE_DATE=$(date -d "$created_at" +%s 2>/dev/null || echo "0")
+
+              if [ "$RELEASE_DATE" != "0" ] && [ "$RELEASE_DATE" -lt "$CUTOFF_DATE" ]; then
+                echo "Deleting old nightly release: $tag (created: $(date -d @$RELEASE_DATE -u +"%Y-%m-%d %H:%M:%S UTC"))"
+                gh release delete "$tag" --yes --repo ${{ github.repository }} 2>/dev/null || true
+                git push origin :refs/tags/"$tag" 2>/dev/null || true
+              else
+                echo "Keeping nightly release: $tag (created: $(date -d @$RELEASE_DATE -u +"%Y-%m-%d %H:%M:%S UTC"))"
+              fi
             done
 
       - name: Generate release notes