fix(p8-security): close review gaps in the ownership gate and copy-as failure propagation

- H3: a daemon module without 'client owner = yes' now also has super-user
  device activity forced off (char/block mknod, --write-devices), so a root
  daemon can no longer be made to create/write raw devices under AUTO.  The
  entries are skipped, preserving ordinary -a pushes.
- H1/H2: propagate a failed required --copy-as chown from symlink metadata
  restore and implicitly-created parent directories, so the entry (and run)
  reports failure instead of a wrong-owner success.
- Docs/help/headers updated for A2/A3 and the device clamp; startup warning
  spells out the client-owner risk.
- Tests: daemon device clamp (skipped without opt-in, created with opt-in),
  updated --super/--fake-super expectations.

src/shared/file.c

@@ -582,8 +582,16 @@ int file_open_secure_parent(const char* path, char** leaf_out, bool create_dirs)
              (a pre-existing destination directory is left alone, matching
              rsync's transferred-entry scope); the helper is a no-op unless an
              identity policy is active. */
-          if (created && identity_copy_as_active())
-            identity_apply_ownership_link(fd, component, 0, 0);
+          if (created && identity_copy_as_active() &&
+              !identity_apply_ownership_link(fd, component, 0, 0)) {
+            /* A REQUIRED --copy-as ownership that cannot be applied to a
+               directory this walk just created must fail the entry rather than
+               leave that implicit parent owned by the receiver. */
+            close(fd);
+            free(copy);
+            free(leaf);
+            return -1;
+          }
           next = openat(fd, component, O_RDONLY | O_DIRECTORY | O_NOFOLLOW | O_CLOEXEC);
         }
       }