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>

gdlintrc

@@ -0,0 +1,47 @@
+class-definitions-order:
+- tools
+- classnames
+- extends
+- docstrings
+- signals
+- enums
+- consts
+- staticvars
+- exports
+- pubvars
+- prvvars
+- onreadypubvars
+- onreadyprvvars
+- others
+class-load-variable-name: (([A-Z][a-z0-9]*)+|_?[a-z][a-z0-9]*(_[a-z0-9]+)*)
+class-name: ([A-Z][a-z0-9]*)+
+class-variable-name: _?[a-z][a-z0-9]*(_[a-z0-9]+)*
+comparison-with-itself: null
+constant-name: _?[A-Z][A-Z0-9]*(_[A-Z0-9]+)*
+disable: []
+duplicated-load: null
+enum-element-name: '[A-Z][A-Z0-9]*(_[A-Z0-9]+)*'
+enum-name: ([A-Z][a-z0-9]*)+
+excluded_directories: !!set
+  .git: null
+expression-not-assigned: null
+function-argument-name: _?[a-z][a-z0-9]*(_[a-z0-9]+)*
+function-arguments-number: 10
+function-name: (_on_([A-Z][a-z0-9]*)+(_[a-z0-9]+)*|_?[a-z][a-z0-9]*(_[a-z0-9]+)*)
+function-preload-variable-name: ([A-Z][a-z0-9]*)+
+function-variable-name: '[a-z][a-z0-9]*(_[a-z0-9]+)*'
+load-constant-name: (([A-Z][a-z0-9]*)+|_?[A-Z][A-Z0-9]*(_[A-Z0-9]+)*)
+loop-variable-name: _?[a-z][a-z0-9]*(_[a-z0-9]+)*
+max-file-lines: 1000
+max-line-length: 100
+max-public-methods: 20
+max-returns: 6
+mixed-tabs-and-spaces: null
+no-elif-return: null
+no-else-return: null
+signal-name: '[a-z][a-z0-9]*(_[a-z0-9]+)*'
+sub-class-name: _?([A-Z][a-z0-9]*)+
+tab-characters: 1
+trailing-whitespace: null
+unnecessary-pass: null
+unused-argument: null