Add flights-map SEO builder and JSON-LD WebPage schema

Phase 4D: buildFlightsMapSeo generates meta tags, canonical, hreflang, OG
and Twitter Card props. buildFlightsMapJsonLd produces a schema.org WebPage
object for structured data. 10 tests cover both builders.

src/features/flights-map/json-ld.ts

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+/**
+ * JSON-LD schema builder for the Flights Map page.
+ *
+ * Produces a schema.org WebPage typed object ready for <JsonLdRenderer>.
+ *
+ * @module
+ */
+
+import type { WebPage } from "schema-dts";
+
+// ---------------------------------------------------------------------------
+// Constants
+// ---------------------------------------------------------------------------
+
+const SITE_NAME = "Aeroflot";
+const PATH_WITHOUT_LOCALE = "/flights-map";
+
+// ---------------------------------------------------------------------------
+// Public
+// ---------------------------------------------------------------------------
+
+/**
+ * Build a schema.org WebPage JSON-LD object for the flights map page.
+ */
+export function buildFlightsMapJsonLd(
+  locale: string,
+  canonicalOrigin: string,
+): WebPage {
+  const url = `${canonicalOrigin}/${locale}${PATH_WITHOUT_LOCALE}`;
+
+  return {
+    "@type": "WebPage",
+    name: `${SITE_NAME} - Flight Map`,
+    url,
+    inLanguage: locale,
+    isPartOf: {
+      "@type": "WebSite",
+      name: SITE_NAME,
+      url: canonicalOrigin,
+    },
+  };
+}

src/features/flights-map/seo.test.ts

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+import { describe, expect, it } from "vitest";
+import { buildFlightsMapSeo } from "./seo.js";
+import { buildFlightsMapJsonLd } from "./json-ld.js";
+
+/** Stub t() that returns the key for assertion. */
+function stubT(key: string): string {
+  return key;
+}
+
+const CANONICAL = "https://www.aeroflot.ru";
+
+// ---------------------------------------------------------------------------
+// buildFlightsMapSeo
+// ---------------------------------------------------------------------------
+
+describe("buildFlightsMapSeo", () => {
+  it("uses FLIGHTS_MAP translation keys", () => {
+    const result = buildFlightsMapSeo(stubT, "ru", CANONICAL);
+
+    expect(result.title).toBe("SEO.FLIGHTS_MAP.TITLE");
+    expect(result.description).toBe("SEO.FLIGHTS_MAP.DESCRIPTION");
+  });
+
+  it("sets canonical to /{locale}/flights-map", () => {
+    const result = buildFlightsMapSeo(stubT, "en", CANONICAL);
+
+    expect(result.canonical).toBe("https://www.aeroflot.ru/en/flights-map");
+  });
+
+  it("includes hreflang with 10 entries", () => {
+    const result = buildFlightsMapSeo(stubT, "ru", CANONICAL);
+
+    expect(result.hreflang).toHaveLength(10);
+  });
+
+  it("sets og tags", () => {
+    const result = buildFlightsMapSeo(stubT, "ru", CANONICAL);
+
+    expect(result.og.title).toBe(result.title);
+    expect(result.og.type).toBe("website");
+    expect(result.og.locale).toBe("ru");
+    expect(result.og.siteName).toBe("Aeroflot");
+    expect(result.og.url).toBe("https://www.aeroflot.ru/ru/flights-map");
+  });
+
+  it("sets twitter card to summary", () => {
+    const result = buildFlightsMapSeo(stubT, "ru", CANONICAL);
+
+    expect(result.twitter).toBeDefined();
+    expect(result.twitter!.card).toBe("summary");
+  });
+});
+
+// ---------------------------------------------------------------------------
+// buildFlightsMapJsonLd
+// ---------------------------------------------------------------------------
+
+describe("buildFlightsMapJsonLd", () => {
+  it("returns a WebPage schema", () => {
+    const result = buildFlightsMapJsonLd("ru", CANONICAL);
+
+    expect(result["@type"]).toBe("WebPage");
+  });
+
+  it("sets the correct URL with locale", () => {
+    const result = buildFlightsMapJsonLd("en", CANONICAL);
+
+    expect(result.url).toBe("https://www.aeroflot.ru/en/flights-map");
+  });
+
+  it("sets inLanguage to the locale", () => {
+    const result = buildFlightsMapJsonLd("ja", CANONICAL);
+
+    expect(result.inLanguage).toBe("ja");
+  });
+
+  it("includes isPartOf WebSite reference", () => {
+    const result = buildFlightsMapJsonLd("ru", CANONICAL);
+
+    expect(result.isPartOf).toBeDefined();
+    const site = result.isPartOf as { "@type": string; name: string; url: string };
+    expect(site["@type"]).toBe("WebSite");
+    expect(site.name).toBe("Aeroflot");
+    expect(site.url).toBe(CANONICAL);
+  });
+
+  it("sets name with site name prefix", () => {
+    const result = buildFlightsMapJsonLd("ru", CANONICAL);
+
+    expect(result.name).toContain("Aeroflot");
+    expect(result.name).toContain("Flight Map");
+  });
+});

src/features/flights-map/seo.ts

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+/**
+ * SEO builder functions for Flights Map route page.
+ *
+ * Pure function -- all data arrives via parameters, no hooks or side effects.
+ * Returns a SeoHeadProps object ready for <SeoHead>.
+ *
+ * @module
+ */
+
+import type { SeoHeadProps } from "@/ui/seo/SeoHead.js";
+import { buildHreflangSet } from "@/shared/seo/hreflang.js";
+
+// ---------------------------------------------------------------------------
+// Types
+// ---------------------------------------------------------------------------
+
+// eslint-disable-next-line @typescript-eslint/no-explicit-any
+export type TFunction = (key: string, opts?: any) => string;
+
+// ---------------------------------------------------------------------------
+// Constants
+// ---------------------------------------------------------------------------
+
+const OG_IMAGE = "https://www.aeroflot.ru/static/images/aeroflot-og-default.png";
+const SITE_NAME = "Aeroflot";
+const PATH_WITHOUT_LOCALE = "/flights-map";
+
+// ---------------------------------------------------------------------------
+// Public
+// ---------------------------------------------------------------------------
+
+/**
+ * SEO props for the Flights Map start page.
+ */
+export function buildFlightsMapSeo(
+  t: TFunction,
+  locale: string,
+  canonicalOrigin: string,
+): SeoHeadProps {
+  const title = t("SEO.FLIGHTS_MAP.TITLE");
+  const description = t("SEO.FLIGHTS_MAP.DESCRIPTION");
+  const canonical = `${canonicalOrigin}/${locale}${PATH_WITHOUT_LOCALE}`;
+
+  return {
+    title,
+    description,
+    canonical,
+    hreflang: buildHreflangSet({
+      canonicalOrigin,
+      pathWithoutLocale: PATH_WITHOUT_LOCALE,
+    }),
+    og: {
+      title,
+      description,
+      url: canonical,
+      image: OG_IMAGE,
+      type: "website",
+      locale,
+      siteName: SITE_NAME,
+    },
+    twitter: {
+      card: "summary",
+    },
+  };
+}