chore: add AGENTS.md, helper scripts, codex templates, and CI

scripts/check.sh

@@ -0,0 +1,19 @@
+#!/usr/bin/env bash
+set -euo pipefail
+
+echo "==> Formatting check"
+if command -v dart >/dev/null 2>&1; then
+  dart format --output=none --set-exit-if-changed .
+else
+  echo "dart not found in PATH" >&2
+  exit 1
+fi
+
+echo "==> Static analysis"
+flutter analyze
+
+echo "==> Tests"
+flutter test
+
+echo "\nAll checks passed."
+