test/docs(apply): §6 M2 structural-divergence journey + design note

`tests/structural_divergence.rs`: a repo that nests a group under a different
parent than the server → `pic plan` shows it `diverged`; a bare apply is
refused (422); `--force-local-structure` reparents to the manifest shape;
`--adopt-server-structure` keeps the server placement. Design doc §6 records M2
shipped, leaving only per-env approval gating deferred.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

crates/picloud-cli/tests/cli.rs

@@ -44,6 +44,7 @@ mod roles;
 mod routes;
 mod scripts;
 mod sealed;
+mod structural_divergence;
 mod secrets;
 mod shared_queues;
 mod shared_topics;