fix(auth): make the owner role real — provisioning, staff doors, panel guards

Found live while verifying the admin email-edit fix: the Owner account could
not load /api/v1/users at all. Root cause: migration 0011 adds the 'owner'
role and gates every user-administration route on it, but NOTHING ever wrote
it. break-glass (UpsertOwner), the setup MC-bind (CompleteOwnerSetup), and the
re-provision path all forced 'admin', so in a fresh install the entire
owner tier — list/create/edit/disable/delete users, quotas, sessions — was
unreachable. The role was a dead letter in the other direction too: staff
predicates that predate the role did not know it.

- UpsertOwner and CompleteOwnerSetup now write role='owner'; the username-
  conflict arm re-asserts it, which is also the documented pre-0011 promotion
  path ("re-provision via break-glass"). InsertOperator stays plain 'admin'.
- Staff doors learn the role: op-login start/finish admit the Owner; the
  player email door refuses it like any staff account; the in-game approver
  check already used staffRole.
- Reclaim protection: IsProtectedAdminLink (and the break-glass bootstrap
  switch AdminExists) count admin OR owner — the Owner must never be displaced
  by a Mojang-priority reclaim.
- Panel guards make migration 0011's claim true now that owner rows exist: an
  owner can never be demoted, deleted, or disabled through the API (only the
  local break-glass console resets the identity); username/email edits still
  work.

Tests: pgint pins both provisioning paths, the protected-link predicate and
the reset/promote semantics; hermetic suites cover the owner-admitting staff
door, the owner-refusing player door, the three panel guards, and break-glass
attribution.

internal/api/middleware.go

@@ -124,7 +124,8 @@ func (a *API) requireExternal(next http.Handler) http.Handler {
 
 // adminOnly gates an external-face handler on the admin Zero-Trust path. The
 // Access middleware has already authenticated; this enforces that admin-tier
-// operations both carry role=admin AND arrived via admin.* (spec §14).
+// operations both carry a staff role (admin or owner) AND arrived via admin.*
+// (spec §14).
 func (a *API) adminOnly(next http.HandlerFunc) http.HandlerFunc {
 	return func(w http.ResponseWriter, r *http.Request) {
 		if p := principalFromContext(r.Context()); !p.IsAdmin() {