usernames: operator reserved-username blocklist

A plain blocklist for names like @support - separate from the collectible
system, so a reservation has no owner, no price and no "bought on Fragment"
badge.

- reserved_usernames table + migration.
- Enforced in replacePeerUsernameTx (the single editable-username write point:
  account.updateUsername, channels.updateUsername, @BotFather /setusername) and
  in the collectible mint path; a reserved name returns USERNAME_OCCUPIED.
- admin.Service: ReserveUsername / UnreserveUsername (journalled commands) and
  the ReservedUsernames listing.
- adminapi: /v1/reserved-usernames{,/reserve,/unreserve}.
- telesrv-admin panel + a "Reserved Usernames" page in the web UI (dist rebuilt).
- Postgres and in-memory store implementations; the memory registry gains an
  optional reserved-name check so tests exercise the same rule.

internal/adminapi/server_test.go

@@ -510,12 +510,30 @@ func (fakeService) ReviewModerationAppeal(context.Context, domain.ModerationDeci
 
 type captureCollectibleUsernameService struct {
 	fakeService
-	mint     admin.MintCollectibleUsernameRequest
-	transfer admin.TransferCollectibleUsernameRequest
-	revoke   admin.RevokeCollectibleUsernameRequest
-	del      admin.DeleteCollectibleUsernameRequest
-	filter   domain.CollectibleUsernameFilter
-	assetID  int64
+	mint      admin.MintCollectibleUsernameRequest
+	transfer  admin.TransferCollectibleUsernameRequest
+	revoke    admin.RevokeCollectibleUsernameRequest
+	del       admin.DeleteCollectibleUsernameRequest
+	reserve   admin.ReserveUsernameRequest
+	unreserve admin.UnreserveUsernameRequest
+	resFilter domain.ReservedUsernameFilter
+	filter    domain.CollectibleUsernameFilter
+	assetID   int64
+}
+
+func (s *captureCollectibleUsernameService) ReserveUsername(_ context.Context, req admin.ReserveUsernameRequest) (admin.CommandResult, error) {
+	s.reserve = req
+	return admin.CommandResult{CommandID: req.CommandID, Status: "completed", DryRun: req.DryRun}, nil
+}
+
+func (s *captureCollectibleUsernameService) UnreserveUsername(_ context.Context, req admin.UnreserveUsernameRequest) (admin.CommandResult, error) {
+	s.unreserve = req
+	return admin.CommandResult{CommandID: req.CommandID, Status: "completed", DryRun: req.DryRun}, nil
+}
+
+func (s *captureCollectibleUsernameService) ReservedUsernames(_ context.Context, filter domain.ReservedUsernameFilter) ([]domain.ReservedUsername, error) {
+	s.resFilter = filter
+	return []domain.ReservedUsername{{Username: "support", Reason: "official", Actor: "ops"}}, nil
 }
 
 func (s *captureCollectibleUsernameService) MintCollectibleUsername(_ context.Context, req admin.MintCollectibleUsernameRequest) (admin.CommandResult, error) {
@@ -731,3 +749,49 @@ func (fakeService) CollectibleUsernameByID(context.Context, int64) (domain.Colle
 func (fakeService) CollectibleUsernameTransfers(context.Context, int64, int) ([]domain.CollectibleUsernameTransfer, error) {
 	return nil, nil
 }
+
+func (fakeService) ReserveUsername(_ context.Context, req admin.ReserveUsernameRequest) (admin.CommandResult, error) {
+	return admin.CommandResult{CommandID: req.CommandID, Status: "completed", DryRun: req.DryRun}, nil
+}
+
+func (fakeService) UnreserveUsername(_ context.Context, req admin.UnreserveUsernameRequest) (admin.CommandResult, error) {
+	return admin.CommandResult{CommandID: req.CommandID, Status: "completed", DryRun: req.DryRun}, nil
+}
+
+func (fakeService) ReservedUsernames(context.Context, domain.ReservedUsernameFilter) ([]domain.ReservedUsername, error) {
+	return nil, nil
+}
+
+func TestAdminAPIReservedUsernames(t *testing.T) {
+	svc := &captureCollectibleUsernameService{}
+	srv := &Server{token: "secret", svc: svc}
+
+	reserve := httptest.NewRequest(http.MethodPost, "/v1/reserved-usernames/reserve", strings.NewReader(
+		`{"command_id":"r-1","actor":"ops","reason":"official","username":"support"}`))
+	reserve.Header.Set("Authorization", "Bearer secret")
+	rec := httptest.NewRecorder()
+	srv.routes().ServeHTTP(rec, reserve)
+	if rec.Code != http.StatusOK || svc.reserve.Username != "support" || svc.reserve.CommandID != "r-1" {
+		t.Fatalf("reserve status=%d req=%+v", rec.Code, svc.reserve)
+	}
+
+	unreserve := httptest.NewRequest(http.MethodPost, "/v1/reserved-usernames/unreserve", strings.NewReader(
+		`{"command_id":"u-1","actor":"ops","reason":"done","username":"support"}`))
+	unreserve.Header.Set("Authorization", "Bearer secret")
+	rec = httptest.NewRecorder()
+	srv.routes().ServeHTTP(rec, unreserve)
+	if rec.Code != http.StatusOK || svc.unreserve.Username != "support" {
+		t.Fatalf("unreserve status=%d req=%+v", rec.Code, svc.unreserve)
+	}
+
+	list := httptest.NewRequest(http.MethodGet, "/v1/reserved-usernames?q=sup&limit=10", nil)
+	list.Header.Set("Authorization", "Bearer secret")
+	rec = httptest.NewRecorder()
+	srv.routes().ServeHTTP(rec, list)
+	if rec.Code != http.StatusOK || !strings.Contains(rec.Body.String(), `"username":"support"`) {
+		t.Fatalf("list status=%d body=%s", rec.Code, rec.Body.String())
+	}
+	if svc.resFilter.Query != "sup" || svc.resFilter.Limit != 10 {
+		t.Fatalf("list filter = %+v", svc.resFilter)
+	}
+}