feat: first version of the interface, integrate Tailwind CSS and update routing

- Add Tailwind CSS dependencies and configure Vite to use Tailwind
- Implement routing with React Router for Landing and Dashboard pages
- Remove unused App.css file and refactor App component to utilize new structure
- Update global styles in index.css to incorporate Tailwind's utility classes

frontend/src/services/api.js

@@ -0,0 +1,146 @@
+/**
+ * Thin API client for the FastAPI backend.
+ *
+ * Every call returns parsed JSON (or a Blob for file downloads) and throws
+ * an `ApiError` on non-2xx responses so callers can decide how to surface it
+ * (toast, inline error, retry, etc.).
+ *
+ * The base URL is injected at build time via `VITE_API_URL`
+ * (see `.env.example`). During development, leaving it blank falls back to
+ * same-origin requests, which plays well with a Vite proxy.
+ */
+
+import {
+  mockExport,
+  mockGetPublications,
+  mockSyncResearcher,
+  mockValidateOrcid,
+} from "./mocks";
+
+const BASE_URL = (import.meta.env.VITE_API_URL ?? "").replace(/\/$/, "");
+
+/**
+ * When the backend is not available yet, set `VITE_USE_MOCKS=true` in your
+ * `.env.local` to route every call through `mocks.js`. In production this
+ * flag MUST be unset.
+ */
+const USE_MOCKS = import.meta.env.VITE_USE_MOCKS === "true";
+
+export class ApiError extends Error {
+  constructor(message, { status, payload } = {}) {
+    super(message);
+    this.name = "ApiError";
+    this.status = status;
+    this.payload = payload;
+  }
+}
+
+async function request(path, { method = "GET", body, signal, headers } = {}) {
+  const url = `${BASE_URL}${path}`;
+  const init = {
+    method,
+    signal,
+    headers: {
+      Accept: "application/json",
+      ...(body ? { "Content-Type": "application/json" } : {}),
+      ...headers,
+    },
+  };
+  if (body !== undefined) init.body = JSON.stringify(body);
+
+  let response;
+  try {
+    response = await fetch(url, init);
+  } catch (cause) {
+    throw new ApiError("No se pudo contactar con el servidor.", {
+      status: 0,
+      payload: { cause: String(cause) },
+    });
+  }
+
+  if (!response.ok) {
+    let payload = null;
+    try {
+      payload = await response.json();
+    } catch {
+      /* response had no JSON body */
+    }
+    const detail =
+      payload?.detail ?? payload?.message ?? response.statusText ?? "Error";
+    throw new ApiError(typeof detail === "string" ? detail : "Error de API", {
+      status: response.status,
+      payload,
+    });
+  }
+
+  if (response.status === 204) return null;
+  const contentType = response.headers.get("content-type") ?? "";
+  if (contentType.includes("application/json")) return response.json();
+  return response;
+}
+
+/* ───────────────────────────── Endpoints ─────────────────────────────── */
+
+/** POST /api/orcid/validate — validates an ORCID iD and returns the researcher. */
+export function validateOrcid(orcidId, { signal } = {}) {
+  if (USE_MOCKS) return mockValidateOrcid(orcidId);
+  return request("/api/orcid/validate", {
+    method: "POST",
+    body: { orcid_id: orcidId },
+    signal,
+  });
+}
+
+/** GET /api/researchers/{orcid}/publications — lists ORCID works. */
+export function getPublications(orcidId, { signal } = {}) {
+  if (USE_MOCKS) return mockGetPublications(orcidId);
+  return request(
+    `/api/researchers/${encodeURIComponent(orcidId)}/publications`,
+    { signal },
+  );
+}
+
+/** POST /api/researchers/{orcid}/sync — triggers ORCID re-harvest. */
+export function syncResearcher(orcidId, { signal } = {}) {
+  if (USE_MOCKS) return mockSyncResearcher(orcidId);
+  return request(`/api/researchers/${encodeURIComponent(orcidId)}/sync`, {
+    method: "POST",
+    signal,
+  });
+}
+
+/**
+ * Builds the public export URL so links/anchors can download files directly
+ * without going through `fetch`. Used by the export dropdown.
+ */
+export function getExportUrl(orcidId, format) {
+  return `${BASE_URL}/api/researchers/${encodeURIComponent(orcidId)}/export/sword.${format}`;
+}
+
+/**
+ * Downloads an export as a Blob (useful when we want to trigger a
+ * programmatic file download). Falls back to `ApiError` on failure.
+ */
+export async function downloadExport(orcidId, format, { signal } = {}) {
+  if (USE_MOCKS) {
+    await mockExport(format);
+    return { blob: null, url: getExportUrl(orcidId, format) };
+  }
+  const url = getExportUrl(orcidId, format);
+  let response;
+  try {
+    response = await fetch(url, { signal });
+  } catch (cause) {
+    throw new ApiError("No se pudo contactar con el servidor.", {
+      status: 0,
+      payload: { cause: String(cause) },
+    });
+  }
+  if (!response.ok) {
+    throw new ApiError(`No se pudo exportar el fichero ${format.toUpperCase()}.`, {
+      status: response.status,
+    });
+  }
+  const blob = await response.blob();
+  return { blob, url };
+}