test: add unit tests for pure logic modules

Add 22 test files covering imager, soundtracks, browser-headers, source-keys (figure/pet/effect), effect-source, plus catalog-translations, catalog-layouts, client-translation-files, translations-utils, and various admin/services/helpers modules. Total test count increases by 120+.

src/lib/services/import/core/browser-headers.test.ts

@@ -0,0 +1,36 @@
+import { describe, expect, it } from "vitest";
+import { browserHeaders } from "./browser-headers";
+
+describe("browserHeaders", () => {
+	it("defaults to empty destination headers", () => {
+		const h = browserHeaders();
+		expect(h["User-Agent"]).toContain("Chrome/125");
+		expect(h["Sec-Fetch-Mode"]).toBe("cors");
+		expect(h["Sec-Fetch-Dest"]).toBe("empty");
+		expect(h["Upgrade-Insecure-Requests"]).toBeUndefined();
+	});
+
+	it("uses navigate mode for documents", () => {
+		const h = browserHeaders("document");
+		expect(h["Sec-Fetch-Mode"]).toBe("navigate");
+		expect(h["Sec-Fetch-Dest"]).toBe("document");
+		expect(h["Upgrade-Insecure-Requests"]).toBe("1");
+		expect(h.Accept).toContain("text/html");
+	});
+
+	it("uses no-cors mode for images", () => {
+		const h = browserHeaders("image");
+		expect(h["Sec-Fetch-Mode"]).toBe("no-cors");
+		expect(h.Accept).toContain("image/avif");
+	});
+
+	it("uses wildcard accept for scripts", () => {
+		expect(browserHeaders("script").Accept).toBe("*/*");
+	});
+
+	it("merges extra headers last", () => {
+		const h = browserHeaders("empty", { "User-Agent": "custom" });
+		expect(h["User-Agent"]).toBe("custom");
+		expect(h.Accept).toContain("application/json");
+	});
+});