POST /admin/users (Site-Admin guard) creates an account with the same
field rules as self-registration, but active immediately: the admin
vouches for the address, so the e-mail is marked verified and the
personal pond is provisioned exactly like the verify-email path does
(markEmailVerified alone would skip the pond).
The user manager gains a create dialog (useModalFocus/useDismissable,
Field wiring, flat RHF field names per the #322 lesson). New audit
action user.created_by_admin, catalogue bumped to 1.9.
Tests: api e2e-db (create + immediate login + personal pond, duplicate
username 409, non-admin 403), web e2e through the dialog, and the
admin a11y scan now opens the dialog too. Both packs verified locally
against a fresh stack.
Closes#331
