feat: enhance authentication flow and UI components

- Updated .env.example to include OAuth authentication details and bypass mode for development.
- Integrated AuthProvider in App component to manage authentication state.
- Added AuthCallbackPage for handling OAuth callback.
- Enhanced ExportDropdown and PublicationsTable components to display new publication indicators for authenticated users.
- Updated AppHeader to show authentication status and logout functionality.
- Improved LandingPage to support group search and simulate login in bypass mode.
- Refactored DashboardPage to conditionally handle publication exports based on user authentication status.

frontend/src/components/dashboard/ExportDropdown.jsx

@@ -4,6 +4,7 @@ import {
   DocumentIcon,
   DownloadIcon,
   PackageIcon,
+  SparkleIcon,
 } from "../ui/Icons";
 import { Spinner } from "../ui/Spinner";
 
@@ -23,17 +24,20 @@ const FORMATS = [
 ];
 
 /**
- * SWORD export dropdown. Delegates the actual download to `onExport(format)`
- * so it can be wired up either to the real API or to a mock layer from the
- * parent page.
+ * SWORD export dropdown. Delegatea the actual download to `onExport(format)`.
  *
- * `exportingFormat` (optional) lets the parent keep the button in a loading
- * state between clicks (e.g. while waiting for the backend blob).
+ * Props:
+ *   - `isAuthenticated`      → cambia el texto del botón principal.
+ *   - `newPublicationsCount` → cuántas publicaciones tiene downloaded_by_me=false.
+ *   - `selectedCount`        → publicaciones seleccionadas manualmente.
+ *   - `exportingFormat`      → formato en curso (pone el botón en loading).
  */
 export function ExportDropdown({
   onExport,
   exportingFormat = null,
   selectedCount = 0,
+  isAuthenticated = false,
+  newPublicationsCount = 0,
 }) {
   const [open, setOpen] = useState(false);
   const rootRef = useRef(null);
@@ -56,19 +60,40 @@ export function ExportDropdown({
     onExport(format);
   }
 
-  const idleLabel = hasSelection
-    ? `Exportar seleccionadas (${selectedCount})`
-    : "Exportar todas";
+  // Label logic:
+  //   manual selection → always "Exportar seleccionadas (N)"
+  //   logged in, no selection → "Descargar lo nuevo (N)" or "Todo descargado"
+  //   not logged in, no selection → "Descargar todo"
+  let idleLabel;
+  let showSparkle = false;
+  if (hasSelection) {
+    idleLabel = `Exportar seleccionadas (${selectedCount})`;
+  } else if (isAuthenticated) {
+    if (newPublicationsCount > 0) {
+      idleLabel = `Descargar lo nuevo (${newPublicationsCount})`;
+      showSparkle = true;
+    } else {
+      idleLabel = "Todo descargado";
+    }
+  } else {
+    idleLabel = "Descargar todo";
+  }
 
   return (
     <div className="relative" ref={rootRef}>
       <button
         type="button"
         onClick={() => setOpen((o) => !o)}
-        disabled={isBusy}
+        disabled={isBusy || (isAuthenticated && !hasSelection && newPublicationsCount === 0)}
         className="inline-flex items-center gap-2 rounded-lg border border-surface-border-strong bg-surface-primary px-[18px] py-2.5 text-sm font-medium text-ink-primary transition-colors enabled:hover:bg-surface-secondary disabled:cursor-not-allowed disabled:opacity-70"
       >
-        {isBusy ? <Spinner size={15} /> : <DownloadIcon />}
+        {isBusy ? (
+          <Spinner size={15} />
+        ) : showSparkle ? (
+          <SparkleIcon size={15} className="text-brand-accent" />
+        ) : (
+          <DownloadIcon />
+        )}
         {isBusy
           ? `Exportando ${exportingFormat.toUpperCase()}...`
           : idleLabel}

frontend/src/components/dashboard/PublicationsTable.jsx

@@ -1,5 +1,5 @@
 import { useEffect, useMemo, useRef, useState } from "react";
-import { AlertIcon, ChevronDownIcon, FilterIcon, SearchIcon } from "../ui/Icons";
+import { AlertIcon, ChevronDownIcon, FilterIcon, SearchIcon, SparkleIcon } from "../ui/Icons";
 import { Spinner } from "../ui/Spinner";
 import { Badge } from "../ui/Badge";
 
@@ -83,6 +83,7 @@ export function PublicationsTable({
   onRetry,
   selectedIds = EMPTY_SELECTION,
   onSelectedIdsChange,
+  isAuthenticated = false,
 }) {
   const [filter, setFilter] = useState("");
   const [sortKey, setSortKey] = useState("publication_year");
@@ -447,7 +448,18 @@ export function PublicationsTable({
                         />
                       </td>
                       <td className="max-w-[280px] px-4 py-3.5 text-[13px] font-medium leading-relaxed text-ink-primary">
-                        {pub.title}
+                        <span className="flex flex-wrap items-start gap-1.5">
+                          {isAuthenticated && pub.downloaded_by_me === false && (
+                            <span
+                              title="No descargada aún por ti"
+                              className="mt-0.5 inline-flex shrink-0 items-center gap-0.5 rounded-full bg-brand-accent/10 px-1.5 py-0.5 text-[10px] font-semibold uppercase tracking-wide text-brand-accent"
+                            >
+                              <SparkleIcon size={9} />
+                              Nuevo
+                            </span>
+                          )}
+                          {pub.title}
+                        </span>
                       </td>
                       <td className="whitespace-nowrap px-4 py-3.5 text-[13px] text-ink-secondary">
                         {pub.journal || "—"}