Add project skeleton: Godot setup, tooling, and smoke test

Pins Godot 4.6.3-stable and GUT 9.6.0 (9.6.1+ reference
AccessibilityServer, unavailable in 4.6.3) via tools/setup.sh. Wires
make check (gdlint + gdformat config for 4-space indent, headless
GUT run, and a JSON well-formedness check ahead of real schema
validation). Seven autoload stubs match the architecture in the
cahier des charges; real logic lands with the following steps.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

.gitignore

@@ -0,0 +1,26 @@
+# Runtime et artefacts Godot
+.godot/
+build/
+
+# Outillage telecharge par `make setup` (Godot, GUT), non versionne
+.godot-bin/
+addons/gut/
+.venv/
+
+# Python
+__pycache__/
+*.pyc
+
+# Secrets et identifiants (export, env, mots de passe, cles)
+.env
+*.env
+*.keystore
+*.jks
+*.p12
+*.mobileprovision
+secrets.*
+export_credentials.cfg
+
+# Fichiers d'edition courants
+*.swp
+.DS_Store