feat(catalog-sync): report sources that can only be compared, not imported

The Habbo presets (and the other furnidata-only sources) carry no
`nitroBaseUrl`, so the clone importer's `${nitroBaseUrl}/${classname}.nitro`
download can never work against them — an `--import-new` run would have failed
for every single item instead of saying why. The SWF path that does work against
`images.habbo.com` lives in `furni-import.ts`, not in the clone importer this
CLI uses.

`stepImportNew` now skips those sources up-front, lists them under
"compared only" in the summary, and the menu prints the same warning when an
import step is chosen with such a source, pointing at the sources that do serve
bundles. Verified: Habbo (COM) reports compare-only, while Habboon and
VirtualCity list real candidates.

scripts/catalog-sync.test.ts

@@ -3,6 +3,7 @@ import { tmpdir } from "node:os";
 import { join } from "node:path";
 import { afterEach, beforeEach, describe, expect, it, vi } from "vitest";
 import {
+	canImportBundles,
 	DEFAULT_CATALOG_SYNC_FLAGS,
 	describeActions,
 	parseCatalogSyncArgs,
@@ -131,6 +132,36 @@ describe("catalog-sync import selection", () => {
 	});
 });
 
+describe("catalog-sync import feasibility", () => {
+	it("imports from a source that serves bundles", () => {
+		expect(
+			canImportBundles({
+				id: "default-habblet-city",
+				name: "Habblet City",
+				furnidataUrl: "https://www.habblet.city/gamedata/furnidata.json",
+				nitroBaseUrl: "https://www.habblet.city/nitro/bundled/furniture",
+				iconBaseUrl: "",
+				hotel: "com",
+			} as never),
+		).toBe(true);
+	});
+
+	// The Habbo presets have no nitro/icon base URL: their furnidata can be
+	// compared, but there is nothing to download from.
+	it("does not import from a compare-only source", () => {
+		expect(
+			canImportBundles({
+				id: "default-habbo-com",
+				name: "Habbo (COM)",
+				furnidataUrl: "https://www.habbo.com/gamedata/furnidata_json/1",
+				nitroBaseUrl: "",
+				iconBaseUrl: "",
+				hotel: "com",
+			} as never),
+		).toBe(false);
+	});
+});
+
 describe("catalog-sync step composition", () => {
 	it("--everything turns on every step except the writing ones", () => {
 		const flags = parseCatalogSyncArgs(["--everything"]);