feat: add local quality gate scripts and documentation

Add quality.sh (bash), quality.ps1 (PowerShell), and fix_format.sh
for automated GDScript quality checking. Includes:
- gdformat --check (formatting gate)
- gdlint (lint rules)
- godot --headless project validation (with 30s timeout)
- Optional GUT test support
- --changed mode for checking only modified .gd files
- Compact summary output with NEXT FIX suggestions
- Full logs saved to logs/quality/latest/

Add docs/local_quality_gate.md with setup and usage instructions.

tools/fix_format.sh

@@ -0,0 +1,24 @@
+#!/usr/bin/env bash
+# fix_format.sh — Auto-format all GDScript files with gdformat.
+# Usage: ./tools/fix_format.sh
+set -euo pipefail
+
+ROOT="$(cd "$(dirname "$0")/.." && pwd)"
+cd "$ROOT"
+
+# detect gdformat
+FMT=""
+if command -v gdformat &>/dev/null; then
+  FMT="gdformat"
+elif python -m gdtoolkit.formatter --help &>/dev/null 2>&1; then
+  FMT="python -m gdtoolkit.formatter"
+fi
+
+if [[ -z "$FMT" ]]; then
+  echo "ERROR: gdformat not found. Install: pip install gdtoolkit"
+  exit 1
+fi
+
+echo "Formatting all .gd files in $ROOT ..."
+$FMT .
+echo "Done."