fix(provisioning): keep the Owner seat single; clash on the operator name stays retryable

Two defects live-drilled in the break-glass staff provisioning:

- An Owner reset that typed any username other than the occupied seat took
  UpsertOwner's insert arm and silently minted a SECOND owner row, leaving the
  existing seat — possibly the compromised account the reset was meant to
  replace — live; every owner row is undeletable through the panel, so the tier
  could never converge back to one. provisionOwner now refuses with
  ownerSeatTakenError naming the seat (recoverable: the TUI routes back to the
  form); bootstrap still mints, and the seat's own username still resets in
  place. PGRepo gains OwnerUsername for the guard.
- InsertOperator returned the raw driver error on a taken username while the
  console keys its rename prompt off api.ErrConflict — the "choose another
  name" leg died with SQLSTATE 23505 against real Postgres (the fake encoded
  the contract; PGRepo had drifted). Map the unique violation to ErrConflict
  and pin it in pgint.

Live (auditfix37): fresh username refused naming the seat; seat reset kept the
id/email with still exactly one owner; taken operator name returned to the form
with the retry note, and the retyped name succeeded (drill rows cleaned).

cmd/felis/breakglass_test.go

@@ -19,14 +19,15 @@ import (
 // terminal. The design is passwordless: accounts carry no credential, and the
 // Owner completes first-login through the setup-token web flow.
 type fakeOwnerStore struct {
-	upserts  []upsertCall
-	inserts  []upsertCall
-	settings map[string][]byte
-	audits   []api.AuditEntry
-	tokens   []setupTokenCall
-	redeems  []redeemCall
-	users    map[string]*api.StaffUser // keyed by username
-	admins   bool                      // AdminExists answer
+	upserts   []upsertCall
+	inserts   []upsertCall
+	settings  map[string][]byte
+	audits    []api.AuditEntry
+	tokens    []setupTokenCall
+	redeems   []redeemCall
+	users     map[string]*api.StaffUser // keyed by username
+	admins    bool                      // AdminExists answer
+	ownerSeat string                    // OwnerUsername answer: the occupied seat, "" when none
 
 	// CompleteOwnerSetup's success result. redeemUserID defaults to the fresh id
 	// the caller passes (the unlinked-UUID case) when left empty.
@@ -40,6 +41,7 @@ type fakeOwnerStore struct {
 	auditErr       error
 	userErr        error // non-not-found error from UserByUsername
 	adminErr       error
+	seatErr        error
 	redeemErr      error
 	createTokenErr error
 }
@@ -80,6 +82,15 @@ func (f *fakeOwnerStore) UserByUsername(_ context.Context, username string) (*ap
 	return nil, api.ErrNotFound
 }
 
+// OwnerUsername reports the single active Owner seat. Tests set ownerSeat; the
+// zero value models a fresh install where bootstrap is free to mint.
+func (f *fakeOwnerStore) OwnerUsername(_ context.Context) (string, error) {
+	if f.seatErr != nil {
+		return "", f.seatErr
+	}
+	return f.ownerSeat, nil
+}
+
 func (f *fakeOwnerStore) UpsertOwner(_ context.Context, id, username, email string) error {
 	if f.upsertErr != nil {
 		return f.upsertErr
@@ -201,6 +212,34 @@ func TestProvisionOwner(t *testing.T) {
 		}
 	})
 
+	t.Run("an occupied seat refuses any other username", func(t *testing.T) {
+		// The seat is the single owner row: upserting a fresh name would take the
+		// insert arm and mint a SECOND owner, while the existing seat — possibly the
+		// compromised account this reset was meant to replace — stays live, and no
+		// supported path can delete an owner row.
+		f := &fakeOwnerStore{ownerSeat: "seat-holder"}
+		err := provisionOwner(ctx, f, "someone-else", "")
+		if !errors.Is(err, api.ErrConflict) {
+			t.Fatalf("error = %v, want it to wrap api.ErrConflict so the TUI routes back to the form", err)
+		}
+		if !strings.Contains(err.Error(), `"seat-holder"`) {
+			t.Errorf("error = %q, want it to name the occupied seat", err)
+		}
+		if len(f.upserts) != 0 {
+			t.Errorf("want no write against an occupied seat, got %d", len(f.upserts))
+		}
+	})
+
+	t.Run("the occupied seat's own username still resets", func(t *testing.T) {
+		f := &fakeOwnerStore{ownerSeat: "seat-holder"}
+		if err := provisionOwner(ctx, f, "seat-holder", "[email protected]"); err != nil {
+			t.Fatalf("provisionOwner(reset): %v", err)
+		}
+		if len(f.upserts) != 1 || f.upserts[0].username != "seat-holder" || f.upserts[0].email != "[email protected]" {
+			t.Fatalf("want 1 reset upsert for the seat, got %+v", f.upserts)
+		}
+	})
+
 	t.Run("propagates a store error", func(t *testing.T) {
 		f := &fakeOwnerStore{upsertErr: errors.New("boom")}
 		if err := provisionOwner(ctx, f, "owner", ""); err == nil {