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.

.gitignore

@@ -74,6 +74,9 @@ ehthumbs_vista.db
 $RECYCLE.BIN/
 *.stackdump
 
+# Local quality gate logs
+logs/quality/
+
 # Linux desktop and trash metadata
 .directory
 .Trash-*