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/Stats.tsx

@@ -3,7 +3,7 @@ import { useTranslation } from "react-i18next";
 import { useMutation, useQuery, useQueryClient } from "@tanstack/react-query";
 import { qk } from "../lib/queryKeys";
 import { History, Pause, Play, RefreshCw } from "lucide-react";
-import { api, type AdminQuotaRow, type Me } from "../lib/api";
+import { api, type AdminQuotaRow } from "../lib/api";
 import { formatEta, formatNumber, formatUnit, quotaActionLabel } from "../lib/format";
 import { notify } from "../lib/notifications";
 import { notifyYouTubeActionError } from "../lib/youtubeErrors";
@@ -61,13 +61,13 @@ export default function Stats() {
         </PageToolbar>
       )}
 
-      {tab === "system" && isAdmin ? <SystemStats /> : <Overview me={me} />}
+      {tab === "system" && isAdmin ? <SystemStats /> : <Overview />}
     </div>
   );
 }
 
-// Per-user view: sync status + your own API usage + (for real accounts) the manual sync actions.
-function Overview({ me }: { me: Me }) {
+// Per-user view: sync status + your own API usage + the manual sync actions.
+function Overview() {
   const { t, i18n } = useTranslation();
   const lang = i18n.language;
   const qc = useQueryClient();
@@ -203,32 +203,30 @@ function Overview({ me }: { me: Me }) {
         )}
       </Section>
 
-      {!me.is_demo && (
-        <Section title={t("stats.sync.actions")}>
-          <div className="flex flex-wrap gap-2">
-            <Tooltip hint={t("stats.sync.syncSubscriptionsHint")}>
-              <Button
-                variant="glass"
-                icon={<RefreshCw />}
-                loading={syncSubs.isPending}
-                onClick={() => syncSubs.mutate()}
-              >
-                {t("stats.sync.syncSubscriptions")}
-              </Button>
-            </Tooltip>
-            <Tooltip hint={t("stats.sync.backfillEverythingHint")}>
-              <Button
-                variant="glass"
-                icon={<History />}
-                loading={deepAll.isPending}
-                onClick={() => deepAll.mutate()}
-              >
-                {t("stats.sync.backfillEverything")}
-              </Button>
-            </Tooltip>
-          </div>
-        </Section>
-      )}
+      <Section title={t("stats.sync.actions")}>
+        <div className="flex flex-wrap gap-2">
+          <Tooltip hint={t("stats.sync.syncSubscriptionsHint")}>
+            <Button
+              variant="glass"
+              icon={<RefreshCw />}
+              loading={syncSubs.isPending}
+              onClick={() => syncSubs.mutate()}
+            >
+              {t("stats.sync.syncSubscriptions")}
+            </Button>
+          </Tooltip>
+          <Tooltip hint={t("stats.sync.backfillEverythingHint")}>
+            <Button
+              variant="glass"
+              icon={<History />}
+              loading={deepAll.isPending}
+              onClick={() => deepAll.mutate()}
+            >
+              {t("stats.sync.backfillEverything")}
+            </Button>
+          </Tooltip>
+        </div>
+      </Section>
     </>
   );
 }