fix: handle symbolic refs in branch pruning script

Skip HEAD -> main symbolic refs that caused git log failures.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

ops/prune-branches.sh

@@ -19,7 +19,7 @@ while [ $# -gt 0 ]; do
 done
 
 CUTOFF=$(date -v-${DAYS}d +%Y-%m-%d 2>/dev/null || date -d "-${DAYS} days" +%Y-%m-%d)
-PROTECTED="main|HEAD"
+PROTECTED="main|HEAD.*"
 
 echo "Scanning $REMOTE for merged branches older than $CUTOFF..."
 echo ""
@@ -32,6 +32,7 @@ DELETE_COUNT=0
 while IFS= read -r branch; do
   branch=$(echo "$branch" | sed 's/^[[:space:]]*//')
   [ -z "$branch" ] && continue
+  echo "$branch" | grep -q ' -> ' && continue
 
   short="${branch#$REMOTE/}"
   echo "$short" | grep -qE "^($PROTECTED)$" && continue