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/src/ffi.rs

@@ -0,0 +1,57 @@
+#![allow(non_camel_case_types, non_snake_case)]
+use std::os::raw::{c_char, c_int, c_void};
+
+pub enum lua_State {}
+pub type lua_Number = f64;
+pub type lua_Integer = i64;
+pub type lua_CFunction = unsafe extern "C" fn(*mut lua_State) -> c_int;
+
+// Constants
+pub const LUA_OK: c_int = 0;
+pub const LUA_TNUMBER: c_int = 3;
+pub const LUA_TSTRING: c_int = 4;
+pub const LUA_MULTRET: c_int = -1;
+
+extern "C" {
+    pub fn luaL_newstate() -> *mut lua_State;
+    pub fn luaL_openlibs(L: *mut lua_State);
+    pub fn lua_close(L: *mut lua_State);
+
+    // Execute
+    pub fn luaL_loadstring(L: *mut lua_State, s: *const c_char) -> c_int;
+    pub fn luaL_loadfilex(L: *mut lua_State, filename: *const c_char, mode: *const c_char) -> c_int;
+    pub fn lua_pcallk(L: *mut lua_State, nargs: c_int, nresults: c_int, msgh: c_int, ctx: isize, k: *const c_void) -> c_int;
+
+    // Stack operations
+    pub fn lua_gettop(L: *mut lua_State) -> c_int;
+    pub fn lua_settop(L: *mut lua_State, idx: c_int);
+    pub fn lua_type(L: *mut lua_State, idx: c_int) -> c_int;
+
+    // Push
+    pub fn lua_pushnumber(L: *mut lua_State, n: lua_Number);
+    pub fn lua_pushstring(L: *mut lua_State, s: *const c_char) -> *const c_char;
+    pub fn lua_pushcclosure(L: *mut lua_State, f: lua_CFunction, n: c_int);
+
+    // Get
+    pub fn lua_tonumberx(L: *mut lua_State, idx: c_int, isnum: *mut c_int) -> lua_Number;
+    pub fn lua_tolstring(L: *mut lua_State, idx: c_int, len: *mut usize) -> *const c_char;
+
+    // Globals
+    pub fn lua_getglobal(L: *mut lua_State, name: *const c_char) -> c_int;
+    pub fn lua_setglobal(L: *mut lua_State, name: *const c_char);
+}
+
+// Helper: lua_pcall macro equivalent
+pub unsafe fn lua_pcall(L: *mut lua_State, nargs: c_int, nresults: c_int, msgh: c_int) -> c_int {
+    lua_pcallk(L, nargs, nresults, msgh, 0, std::ptr::null())
+}
+
+// Helper: lua_pop
+pub unsafe fn lua_pop(L: *mut lua_State, n: c_int) {
+    lua_settop(L, -n - 1);
+}
+
+// Helper: lua_tostring (without length)
+pub unsafe fn lua_tostring(L: *mut lua_State, idx: c_int) -> *const c_char {
+    lua_tolstring(L, idx, std::ptr::null_mut())
+}