refactor: add main.ts decomposition guardrails and extract core helpers

scripts/check-main-lines.sh

@@ -0,0 +1,25 @@
+#!/usr/bin/env bash
+set -euo pipefail
+
+target="${1:-1500}"
+file="${2:-src/main.ts}"
+
+if [[ ! -f "$file" ]]; then
+  echo "[ERROR] File not found: $file" >&2
+  exit 1
+fi
+
+if ! [[ "$target" =~ ^[0-9]+$ ]]; then
+  echo "[ERROR] Target line count must be an integer. Got: $target" >&2
+  exit 1
+fi
+
+actual="$(wc -l < "$file" | tr -d ' ')"
+
+echo "[INFO] $file lines: $actual (target: <= $target)"
+if (( actual > target )); then
+  echo "[ERROR] Line gate failed: $actual > $target" >&2
+  exit 1
+fi
+
+echo "[OK] Line gate passed"