fix: recover gracefully from stale sessions causing repeated 401s

The SPA's session check (/api/auth/session) is cached indefinitely by
react-query (staleTime: Infinity, no refetch on focus/interval), so once a
protected page mounts successfully, the app never re-verifies auth. If the
server-side session later becomes invalid (server restart with in-memory
sessions, cookie/session expiry, etc.), every subsequent API call
(pages, scheduled-posts, audio-tracks, media, media/upload, ...) starts
failing with 401 in a loop with no way for the user to recover short of a
manual page reload.

Add a shared handleUnauthorized() in queryClient.ts that redirects to
/login on any non-auth API 401, wired into both the shared fetch helpers
(apiRequest/getQueryFn) and the raw fetch() calls used for file uploads
and Remotion rendering, which also lacked this recovery path. Also add the
missing credentials: "include" to those raw fetch() calls for consistency
with the rest of the app's API requests.

client/src/pages/new-post.tsx

@@ -31,7 +31,7 @@ import { Checkbox } from "@/components/ui/checkbox";
 import { Select, SelectContent, SelectItem, SelectTrigger, SelectValue } from "@/components/ui/select";
 import { Dialog, DialogContent } from "@/components/ui/dialog";
 import { useToast } from "@/hooks/use-toast";
-import { apiRequest, queryClient } from "@/lib/queryClient";
+import { apiRequest, queryClient, handleUnauthorized } from "@/lib/queryClient";
 import { MediaThumbnail } from "@/components/media-thumbnail";
 import type { SocialPage, Media, ScheduledPost } from "@shared/schema";
 import { PreviewModal } from "@/components/preview-modal";
@@ -148,8 +148,12 @@ export default function NewPost() {
       const response = await fetch("/api/media/upload", {
         method: "POST",
         body: formData,
+        credentials: "include",
       });
-      if (!response.ok) throw new Error("Upload failed");
+      if (!response.ok) {
+        if (response.status === 401) handleUnauthorized("/api/media/upload");
+        throw new Error("Upload failed");
+      }
       return response.json();
     },
     onSuccess: (data) => {