feat(lang): L3 module scope - module, export, friend module

A barrel's 'module NAME' makes its directory a module; a declaration other modules
use says 'export'. Private use from another module is an error naming the module
and where to mark it; 'friend module' sees everything (a test harness); a file in
no module is public and a package keeps its own module. LUDIC_VIS_REPORT=1 lists
every violation instead of stopping, so a codebase can be given its exports first.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

selfhost/backend/game/emit_game.ludic

@@ -658,6 +658,8 @@ function emit_event_fns() -> void {
         g_term = false
         let next = lbl("evnext")
         g_ret_label = next
+        g_err_file = g_onlisten[i].file
+        vis_check(ev, en)
         emit_block(g_onlisten[i].a)
         g_ret_label = "ret"
         if not g_term { emit(`  br label %{next}\n`) }