feat(script): add voltex_script crate with Lua 5.4 FFI and safe wrapper

Compiles Lua 5.4 from source via cc crate (excluding lua.c/luac.c).
Provides ffi bindings, LuaState safe wrapper, and default engine bindings.
All 9 tests pass (exec, globals, register_fn, voltex_print).

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

crates/voltex_script/build.rs

@@ -0,0 +1,19 @@
+fn main() {
+    let mut build = cc::Build::new();
+    build.include("lua");
+
+    // Add all .c files except lua.c and luac.c (standalone executables with main())
+    for entry in std::fs::read_dir("lua").unwrap() {
+        let path = entry.unwrap().path();
+        if let Some(ext) = path.extension() {
+            if ext == "c" {
+                let name = path.file_name().unwrap().to_str().unwrap();
+                if name != "lua.c" && name != "luac.c" {
+                    build.file(&path);
+                }
+            }
+        }
+    }
+
+    build.compile("lua54");
+}