feat(client): gdUnit4 CI runner script (#205)

Headless test runner that delegates to GdUnitTestCIRunner for CI
integration. Exit code 0 = all pass, non-zero = failures per D-030.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

client/tests/run_gdunit4.gd

@@ -0,0 +1,30 @@
+#!/usr/bin/env -S godot -s
+## gdUnit4 CI runner for the Settled Reach client.
+##
+## Run all client tests headlessly:
+##   godot --headless --path client/ \
+##     -s res://tests/run_gdunit4.gd \
+##     -- --ignoreHeadlessMode -a res://tests/
+##
+## Run a specific test file:
+##   godot --headless --path client/ \
+##     -s res://tests/run_gdunit4.gd \
+##     -- --ignoreHeadlessMode -a res://tests/test_protocol.gd
+##
+## Exit code: 0 = all pass, non-zero = failures.
+##
+## D-030 (architecture.md): gdUnit4 is the confirmed Godot test framework.
+## Test output format: JSON summary per D-030 sub-decision #6.
+extends SceneTree
+
+var _cli_runner: GdUnitTestCIRunner
+
+
+func _initialize() -> void:
+	DisplayServer.window_set_mode(DisplayServer.WINDOW_MODE_MINIMIZED)
+	_cli_runner = GdUnitTestCIRunner.new()
+	root.add_child(_cli_runner)
+
+
+func _finalize() -> void:
+	queue_delete(_cli_runner)