wwfixture: declarative fixture runner

Discovers test/wcc/data, hard-pins corpus identity (1,224 fixtures,
314 error / 12 compile / 136 run / 762 run-exit, sha256 name hash),
schedules both frontend cells per fixture through os.exec with
per-cell capture dirs, and emits the strict wwfix TSV result stream.
integration.sh is the black-box owner of the CLI/protocol boundary.

cmd/wwfixture/wwfixture.ww

@@ -0,0 +1,8 @@
+package main;
+
+import os;
+import wwfixture;
+
+export fn main() int = {
+	return wwfixture.command(os.args());
+};