test(11-01): add failing ResultsList spec + extend tender-radar-api client (RED)

Extends tender-radar-api.ts with the Tender type, listTenders(params)
and fetchCoverage() (plain fetch, credentials:'include', matching the
established fetchSourceConfig pattern — TanStack Query is not installed).

Adds the RED-first ResultsList.test.tsx: render items with
title/buyerName/deadline/value, "keine Wertangabe" for null estimatedValue
(D-05), and an empty-state message. ResultsList.tsx does not exist yet.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

apps/web/src/lib/tender-radar-api.ts

@@ -33,6 +33,44 @@ export interface SaveSourceConfigPayload {
   isActive: boolean;
 }
 
+/**
+ * A single tender row from the global `Tender` catalog (Plan 11-01).
+ * `estimatedValue` arrives as a string (Prisma Decimal serializes via
+ * `toJSON()` -> `toString()`), NOT a number — never `Number()`-coerce it
+ * without a null check (D-05: 91.6% of rows are null, "keine Wertangabe").
+ * Date fields arrive as ISO strings (JSON has no native Date type).
+ */
+export interface Tender {
+  id: string;
+  sourcePortal: string;
+  title: string;
+  buyerName: string | null;
+  cpvCodes: string[];
+  region: string | null;
+  plz: string | null;
+  bundesland: string | null;
+  deadlineAt: string | null;
+  estimatedValue: string | null;
+  procedureType: string | null;
+  status: string;
+  sourceUrl: string | null;
+  publishedAt: string;
+}
+
+/** Response shape of GET /modules/tender-radar. */
+export interface ListTendersResponse {
+  items: Tender[];
+  total: number;
+  page: number;
+  limit: number;
+}
+
+/** Response shape of GET /modules/tender-radar/coverage (D-12, UI-05). */
+export interface CoverageResponse {
+  total: number;
+  sources: Array<{ sourcePortal: string; count: number }>;
+}
+
 // --- API functions ---
 
 /**
@@ -65,3 +103,36 @@ export async function saveSourceConfig(
   if (!res.ok) throw new Error('Failed to save tender-radar source config');
   return res.json();
 }
+
+/**
+ * List the global tender catalog with the given filter/sort/pagination
+ * params (Plan 11-01, FILTER-01/04/05, UI-01). `params` mirrors the
+ * TenderQueryDto query-string contract exactly — the URL is the single
+ * source of truth for filter state (Research: URL-Param-getriebener Client).
+ * GET /modules/tender-radar?<params>
+ */
+export async function listTenders(
+  params: URLSearchParams,
+): Promise<ListTendersResponse> {
+  const query = params.toString();
+  const res = await fetch(
+    `${API_URL}/modules/tender-radar${query ? `?${query}` : ''}`,
+    { credentials: 'include' },
+  );
+  if (!res.ok) throw new Error('Failed to fetch tenders');
+  return res.json();
+}
+
+/**
+ * Fetch the active-tender distribution by sourcePortal (D-12, UI-05) —
+ * feeds CoverageBanner so a thin/single-source result list is not
+ * misread as a defect.
+ * GET /modules/tender-radar/coverage
+ */
+export async function fetchCoverage(): Promise<CoverageResponse> {
+  const res = await fetch(`${API_URL}/modules/tender-radar/coverage`, {
+    credentials: 'include',
+  });
+  if (!res.ok) throw new Error('Failed to fetch tender-radar coverage');
+  return res.json();
+}