feat!: remove the shared demo account

The demo account — one shared user that whitelisted emails entered from
the login page, reset on a schedule — goes end to end (owner decision,
E34): demo.py and the reset job, users.is_demo and demo_whitelist
(migration 0098 deletes the demo user, its audit rows, the reset job's
override and notices, then drops the column and table; the downgrade
restores the empty schema), the /auth/demo entry, the admin whitelist and
reset, the Demo tab, the banner, the login page's "Try the demo", and
every is_demo branch in routes, userscope, scheduler and the UI.

require_human only ever refused the demo account, so its 87 uses become
current_user (owner-approved); require_write_scope keeps its own check.
The login page's "or" divider now shows only beside the Google button:
without the demo entry under it, an instance without Google would have
said "or" to nothing.

A contract test (removedFeatures) fails on the word anywhere in the
backend, frontend, e2e or scripts — seen red on a planted hit. Size
ceilings tightened for the modules that shrank; admin.py is back under
the limit.

frontend/src/components/useVideoActions.tsx

@@ -1,6 +1,6 @@
 import { useState } from "react";
 import { useTranslation } from "react-i18next";
-import { useQuery, useQueryClient } from "@tanstack/react-query";
+import { useQuery } from "@tanstack/react-query";
 import {
   Bookmark,
   BookmarkX,
@@ -17,7 +17,7 @@ import {
   Undo2,
 } from "lucide-react";
 
-import { api, type Me, type Video, type VideoStatus } from "../lib/api";
+import { api, type Video, type VideoStatus } from "../lib/api";
 import { isResettable } from "../lib/api/feed";
 import { qk } from "../lib/queryKeys";
 import { pinVideo, useComfortPin } from "./comfortPin";
@@ -48,17 +48,13 @@ const icon = "w-4 h-4";
  *  panel to render beside the menu (one per list). */
 export function useVideoActions(handlers: VideoActionHandlers, open: boolean) {
   const { t } = useTranslation();
-  const qc = useQueryClient();
   const { openChannel } = useNavigationActions();
   const pin = useComfortPin(open);
   const copy = useCopyItems();
-  // Downloads spend server disk and need a real identity: the demo account has none (as the
-  // player's DownloadButton).
-  const canDownload = !qc.getQueryData<Me>(qk.me())?.is_demo;
   const index = useQuery({
     queryKey: qk.downloadIndex(),
     queryFn: api.downloadIndex,
-    enabled: open && canDownload,
+    enabled: open,
     staleTime: 10000,
   });
   const [followUp, setFollowUp] = useState<VideoFollowUpState | null>(null);
@@ -139,17 +135,13 @@ export function useVideoActions(handlers: VideoActionHandlers, open: boolean) {
             },
           ]
         : []),
-      ...(canDownload
-        ? [
-            {
-              id: "download",
-              label: t("downloads.menu.download"),
-              note: dlState,
-              icon: <Download className={icon} />,
-              onSelect: () => setFollowUp({ kind: "download", video: v }),
-            },
-          ]
-        : []),
+      {
+        id: "download",
+        label: t("downloads.menu.download"),
+        note: dlState,
+        icon: <Download className={icon} />,
+        onSelect: () => setFollowUp({ kind: "download", video: v }),
+      },
       ...(details
         ? [
             {