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/admin/service_test.go

@@ -12,6 +12,7 @@ import (
 
 	usernamesapp "telesrv/internal/app/usernames"
 	"telesrv/internal/domain"
+	"telesrv/internal/store/memory"
 )
 
 // Compile-time proof that the shipped use-case services satisfy the admin ports.
@@ -1427,3 +1428,76 @@ func TestDeleteCollectibleUsernameCommand(t *testing.T) {
 		t.Fatalf("delete of invalid name = nil error, want rejection")
 	}
 }
+
+func TestReserveAndUnreserveUsername(t *testing.T) {
+	ctx := context.Background()
+	reserved := memory.NewReservedUsernameStore()
+	svc := NewService(Dependencies{
+		Commands:          newMemoryCommandRepo(),
+		ReservedUsernames: reserved,
+		Now:               fixedNow,
+	})
+
+	dry, err := svc.ReserveUsername(ctx, ReserveUsernameRequest{
+		CommandMeta: CommandMeta{CommandID: "rv-dry", Actor: "ops", Reason: "official handle", DryRun: true},
+		Username:    "@Support",
+	})
+	if err != nil {
+		t.Fatalf("dry-run reserve: %v", err)
+	}
+	if got, _ := reserved.IsReserved(ctx, "support"); got {
+		t.Fatal("dry-run reserved the name")
+	}
+	if dry.Details["username"] != "Support" {
+		t.Fatalf("dry-run details = %+v", dry.Details)
+	}
+
+	if _, err := svc.ReserveUsername(ctx, ReserveUsernameRequest{
+		CommandMeta: CommandMeta{CommandID: "rv-exec", Actor: "ops", Reason: "official handle"},
+		Username:    "support",
+	}); err != nil {
+		t.Fatalf("reserve: %v", err)
+	}
+	if got, _ := reserved.IsReserved(ctx, "support"); !got {
+		t.Fatal("name not reserved after exec")
+	}
+
+	if _, err := svc.UnreserveUsername(ctx, UnreserveUsernameRequest{
+		CommandMeta: CommandMeta{CommandID: "urv-exec", Actor: "ops", Reason: "no longer needed"},
+		Username:    "SUPPORT",
+	}); err != nil {
+		t.Fatalf("unreserve: %v", err)
+	}
+	if got, _ := reserved.IsReserved(ctx, "support"); got {
+		t.Fatal("name still reserved after unreserve")
+	}
+
+	if _, err := svc.ReserveUsername(ctx, ReserveUsernameRequest{
+		CommandMeta: CommandMeta{CommandID: "bad", Actor: "ops", Reason: "x"},
+		Username:    "ab",
+	}); err == nil {
+		t.Fatal("reserve of a too-short name = nil error, want rejection")
+	}
+}
+
+func TestMemoryRegistryRefusesReservedName(t *testing.T) {
+	ctx := context.Background()
+	reserved := memory.NewReservedUsernameStore()
+	if _, err := reserved.ReserveUsername(ctx, "support", "", "ops"); err != nil {
+		t.Fatalf("seed reserve: %v", err)
+	}
+	registry := memory.NewCollectibleUsernameStore().WithReservedUsernames(reserved)
+
+	if _, err := registry.SetEditableUsername(ctx, domain.Peer{Type: domain.PeerTypeUser, ID: 1}, "support"); !errors.Is(err, domain.ErrUsernameOccupied) {
+		t.Fatalf("SetEditableUsername(reserved) err = %v, want ErrUsernameOccupied", err)
+	}
+	if _, _, err := registry.MintCollectibleUsername(ctx, domain.MintCollectibleUsernameRequest{
+		Username: "support", Currency: domain.CollectibleCurrencyUSD, Amount: 0, CommandKey: "k1",
+	}); !errors.Is(err, domain.ErrUsernameOccupied) {
+		t.Fatalf("Mint(reserved) err = %v, want ErrUsernameOccupied", err)
+	}
+	// A different name is unaffected.
+	if _, err := registry.SetEditableUsername(ctx, domain.Peer{Type: domain.PeerTypeUser, ID: 1}, "freename"); err != nil {
+		t.Fatalf("SetEditableUsername(free) err = %v", err)
+	}
+}