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>

project.godot

@@ -0,0 +1,26 @@
+; Engine configuration file.
+; It's best edited using the editor UI and not directly,
+; since the parameters that go here are not all obvious.
+;
+; Format:
+;   [section] ; section goes between []
+;   param=value ; assign values to parameters
+
+config_version=5
+
+[application]
+
+config/name="Les Aventuriers des mots"
+run/main_scene="res://scenes/boot/boot.tscn"
+config/features=PackedStringArray("4.6", "Forward Plus")
+config/icon="res://icon.svg"
+
+[autoload]
+
+GameManager="*res://autoload/game_manager.gd"
+ProfileManager="*res://autoload/profile_manager.gd"
+ProgressManager="*res://autoload/progress_manager.gd"
+ExerciseEngine="*res://autoload/exercise_engine.gd"
+SaveManager="*res://autoload/save_manager.gd"
+AudioManager="*res://autoload/audio_manager.gd"
+SettingsManager="*res://autoload/settings_manager.gd"