refactor: extract ensure_blocked_label_id to lib/ci-helpers.sh (#352)

Move ensure_blocked_label_id() from dev/phase-handler.sh into
lib/ci-helpers.sh to eliminate the duplicate blocked-label creation
curl block that existed in both phase-handler.sh and dev-poll.sh.

Both dev-agent.sh and action-agent.sh now source lib/ci-helpers.sh
so the function is available when phase-handler.sh calls it.

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

dev/dev-poll.sh

@@ -89,16 +89,7 @@ is_blocked() {
 _post_ci_blocked_comment() {
   local issue_num="$1" pr_num="$2" attempts="$3"
   local blocked_id
-  blocked_id=$(codeberg_api GET "/labels" 2>/dev/null \
-    | jq -r '.[] | select(.name == "blocked") | .id' 2>/dev/null || true)
-  if [ -z "$blocked_id" ]; then
-    blocked_id=$(curl -sf -X POST \
-      -H "Authorization: token ${CODEBERG_TOKEN}" \
-      -H "Content-Type: application/json" \
-      "${CODEBERG_API}/labels" \
-      -d '{"name":"blocked","color":"#e11d48"}' 2>/dev/null \
-      | jq -r '.id // empty' 2>/dev/null || true)
-  fi
+  blocked_id=$(ensure_blocked_label_id)
   [ -z "$blocked_id" ] && return 0
 
   local comment