Use wrapper script for label operations in issue triage

Extract triage prompt into /triage-issue command and use a dedicated
edit-issue-labels.sh script for label operations instead of raw
gh issue edit. The script validates labels against the repo's existing
labels before applying them.

scripts/edit-issue-labels.sh

@@ -0,0 +1,87 @@
+#!/usr/bin/env bash
+#
+# Edits labels on a GitHub issue.
+# Usage: ./edit-issue-labels.sh --issue 123 --add-label bug --add-label needs-triage --remove-label untriaged
+#
+
+set -euo pipefail
+
+ISSUE=""
+ADD_LABELS=()
+REMOVE_LABELS=()
+
+# Parse arguments
+while [[ $# -gt 0 ]]; do
+  case $1 in
+    --issue)
+      ISSUE="$2"
+      shift 2
+      ;;
+    --add-label)
+      ADD_LABELS+=("$2")
+      shift 2
+      ;;
+    --remove-label)
+      REMOVE_LABELS+=("$2")
+      shift 2
+      ;;
+    *)
+      exit 1
+      ;;
+  esac
+done
+
+# Validate issue number
+if [[ -z "$ISSUE" ]]; then
+  exit 1
+fi
+
+if ! [[ "$ISSUE" =~ ^[0-9]+$ ]]; then
+  exit 1
+fi
+
+if [[ ${#ADD_LABELS[@]} -eq 0 && ${#REMOVE_LABELS[@]} -eq 0 ]]; then
+  exit 1
+fi
+
+# Fetch valid labels from the repo
+VALID_LABELS=$(gh label list --limit 500 --json name --jq '.[].name')
+
+# Filter to only labels that exist in the repo
+FILTERED_ADD=()
+for label in "${ADD_LABELS[@]}"; do
+  if echo "$VALID_LABELS" | grep -qxF "$label"; then
+    FILTERED_ADD+=("$label")
+  fi
+done
+
+FILTERED_REMOVE=()
+for label in "${REMOVE_LABELS[@]}"; do
+  if echo "$VALID_LABELS" | grep -qxF "$label"; then
+    FILTERED_REMOVE+=("$label")
+  fi
+done
+
+if [[ ${#FILTERED_ADD[@]} -eq 0 && ${#FILTERED_REMOVE[@]} -eq 0 ]]; then
+  exit 0
+fi
+
+# Build gh command arguments
+GH_ARGS=("issue" "edit" "$ISSUE")
+
+for label in "${FILTERED_ADD[@]}"; do
+  GH_ARGS+=("--add-label" "$label")
+done
+
+for label in "${FILTERED_REMOVE[@]}"; do
+  GH_ARGS+=("--remove-label" "$label")
+done
+
+gh "${GH_ARGS[@]}"
+
+if [[ ${#FILTERED_ADD[@]} -gt 0 ]]; then
+  echo "Added: ${FILTERED_ADD[*]}"
+fi
+if [[ ${#FILTERED_REMOVE[@]} -gt 0 ]]; then
+  echo "Removed: ${FILTERED_REMOVE[*]}"
+fi