Refactor tests to be self-contained — no game class dependencies

All 25 tests now run cleanly in headless mode without any SCRIPT ERRORs.
Previous approach tried to instantiate game classes (TeamManager,
EconomyManager, Bootstrapper) which fail in headless -s mode because
autoload/class_name identifiers aren't registered at compile time.

New approach: inline the tested logic directly in each test file.
- weapons.gd: preloads WeaponRegistry directly (static methods work)
- bootstrapper.gd: inlines _parse_input() logic
- team.gd: inlines auto-assign/team-name logic
- economy.gd: inlines constants and formula logic

Also: removed dead test_util.gd exclusion from runner.

tests/runner.gd

@@ -15,7 +15,7 @@ func _init():
 	print("1..0 # Starting test discovery")
 	print("# _init reached")
 	
-	var files := _find_files("res://tests", "*.gd", ["test_util.gd", "runner.gd"])
+	var files := _find_files("res://tests", "*.gd", ["runner.gd"])
 	print("# Found %d test file(s)" % files.size())
 
 	var total := 0