feat(#145): switch dashboard to show last-activity documents

Replace recent-by-creation fetch with GET /api/documents/recent-activity
(sorted by updatedAt) in the dashboard. Update DashboardRecentDocuments
component to use doc.updatedAt, update i18n heading to "Zuletzt aktiv" /
"Recent Activity" / "Actividad reciente", and regenerate API types.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

frontend/src/lib/generated/api.ts

@@ -628,6 +628,22 @@ export interface paths {
         patch?: never;
         trace?: never;
     };
+    "/api/documents/recent-activity": {
+        parameters: {
+            query?: never;
+            header?: never;
+            path?: never;
+            cookie?: never;
+        };
+        get: operations["getRecentActivity"];
+        put?: never;
+        post?: never;
+        delete?: never;
+        options?: never;
+        head?: never;
+        patch?: never;
+        trace?: never;
+    };
     "/api/documents/incomplete": {
         parameters: {
             query?: never;
@@ -2328,6 +2344,28 @@ export interface operations {
             };
         };
     };
+    getRecentActivity: {
+        parameters: {
+            query?: {
+                size?: number;
+            };
+            header?: never;
+            path?: never;
+            cookie?: never;
+        };
+        requestBody?: never;
+        responses: {
+            /** @description OK */
+            200: {
+                headers: {
+                    [name: string]: unknown;
+                };
+                content: {
+                    "*/*": components["schemas"]["Document"][];
+                };
+            };
+        };
+    };
     getIncomplete: {
         parameters: {
             query?: {