w6c+selfhost: cross-module same-leaf type disambiguation via Sym.mod

test/wcc/data/modcollision/mod2/mod2.ww

@@ -0,0 +1,12 @@
+// modcollision/mod2 — exports `type stream` with mod2-shaped fields.
+// Paired with mod1/mod1.ww to exercise same-leaf-name cross-module
+// type disambiguation. Test driver: 696_modtype_leaf_collision.c.
+//
+// Fields are intentionally named distinctly from mod1's (c/d vs a/b)
+// so the negative test (`b: mod1.stream` accessed via mod2-only field
+// 'c') surfaces as a compile-time field-resolution error.
+
+export type stream = struct {
+	c: i32,
+	d: i32,
+};