Phase 0: scaffold e_iwd Enlightenment module

Meson build, module entry points, and stub layout for the iwd backend
(D-Bus client, gadget, popup, config, UI widgets). Bodies are TODOs;
this compiles against EFL/E headers but performs no D-Bus work yet.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

src/e_mod_gadget.h

@@ -0,0 +1,8 @@
+#ifndef E_MOD_GADGET_H
+#define E_MOD_GADGET_H
+
+void e_iwd_gadget_init(void);
+void e_iwd_gadget_shutdown(void);
+void e_iwd_gadget_update(void);
+
+#endif