feat(cli): pic groups (tree/create/rename/reparent/rm/members)

Adds the `pic groups` command family over /api/v1/admin/groups:
ls/tree, create (--parent), show (path + subgroups + apps), rename
(name/description; slug frozen), reparent (--to), rm (--recursive,
leaf-first; never auto-deletes apps), and members add/set/rm/ls. Also
`pic apps create --group <slug>` to place an app under a group.

End-to-end journey tests (tests/groups.rs, DB-gated) cover tree CRUD,
delete=RESTRICT (409 on a non-empty group), reparent cycle rejection, and
the headline invariant: a group_admin on an ancestor group can deploy to
an app it is NOT a direct member of (inherited membership), and loses that
access immediately on revoke — all green against a live server.

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

crates/picloud-cli/tests/cli.rs

@@ -23,6 +23,7 @@ mod dead_letters;
 mod email_queue;
 mod enabled;
 mod env_overlay;
+mod groups;
 mod init;
 mod invoke;
 mod logs;