added lua check CI step

.luacheckrc

@@ -0,0 +1,22 @@
+std = "lua51"
+
+max_line_length = false
+
+-- Compiled bundle is a single file; each source file's locals live inside
+-- their own `do ... end` block, so cross-file shadowing isn't a real risk.
+unused_args = false
+
+-- Cross-file globals set by Spearhead itself (no `require`/module system in the bundle)
+globals = {
+    "SpearheadConfig",
+    "GlobalCapCallBacks",
+    "SpearheadAPI",
+}
+
+-- DCS Mission Scripting Environment API
+read_globals = {
+    "env", "timer", "trigger", "world", "coalition", "country",
+    "AI", "Group", "Unit", "StaticObject", "SceneryObject",
+    "Airbase", "Weapon", "land", "atmosphere", "missionCommands",
+    "net",
+}