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/ChannelPage.tsx

@@ -152,18 +152,17 @@ export default function ChannelPage({
     [channelId, qc, t],
   );
 
-  // First visit of an un-subscribed channel → ingest its recent uploads. Skipped for the demo
-  // account (explore spends shared quota) and when videos are already present (a revisit, or a
-  // subscribed channel whose uploads the scheduler backfills).
+  // First visit of an un-subscribed channel → ingest its recent uploads. Skipped when videos are
+  // already present (a revisit, or a subscribed channel whose uploads the scheduler backfills).
   useEffect(() => {
-    if (!ch || me.is_demo) return;
+    if (!ch) return;
     if (autoTried.current === channelId) return;
     if (ch.subscribed || ch.blocked) return;
     if (ch.explored && ch.stored_videos > 0) return;
     autoTried.current = channelId;
     // eslint-disable-next-line react-hooks/set-state-in-effect -- a one-off INGEST of an unsubscribed channel's uploads on first visit — a network side effect, not state. The autoTried ref keyed on the channel id is what makes it once per channel.
     void runExplore();
-  }, [ch, channelId, me.is_demo, runExplore]);
+  }, [ch, channelId, runExplore]);
 
   const block = useMutation({
     mutationFn: () => (ch?.blocked ? api.unblockChannel(channelId) : api.blockChannel(channelId)),
@@ -238,9 +237,9 @@ export default function ChannelPage({
   // Personal tags, editable right here (the same control + flow the channel manager uses). Optimistic
   // on this channel's detail cache; a failed attach/detach reverts by refetching, and a success
   // invalidates the manager list so a tag added here shows there too.
-  // Only fetch the tag catalog when the editor will actually render (subscribed, non-demo) — an
-  // unsubscribed/demo channel page never shows the control, so the request would be thrown away.
-  const tagsQuery = useTags({ enabled: !!ch?.subscribed && !me.is_demo });
+  // Only fetch the tag catalog when the editor will actually render (subscribed) — an unsubscribed
+  // channel page never shows the control, so the request would be thrown away.
+  const tagsQuery = useTags({ enabled: !!ch?.subscribed });
   const userTags = (tagsQuery.data ?? []).filter((tg) => !tg.system);
   const { toggleTag, createAndAttachTag } = useChannelTagActions({
     optimisticToggle: (id, tagId, attach) =>
@@ -503,7 +502,7 @@ export default function ChannelPage({
                     <SlidersHorizontal className="w-4 h-4" />
                   </IconButton>
                 )}
-                {ch?.subscribed && !me.is_demo && (
+                {ch?.subscribed && (
                   <div className="inline-flex items-center gap-1.5 h-9 px-2.5 rounded-lg border border-border">
                     <span className="text-xs text-muted">{t("channels.cols.priority")}</span>
                     <PriorityStepper
@@ -520,7 +519,7 @@ export default function ChannelPage({
                 While loading, the label carries the live stored/total count (the detail poll refreshes
                 it) so a large channel's paced tail reads as visible progress rather than a stuck
                 spinner. */}
-                {ch?.subscribed && !ch.backfill_done && !me.is_demo && (
+                {ch?.subscribed && !ch.backfill_done && (
                   <Button
                     variant="outline"
                     onClick={() => !ch.deep_requested && deepBackfill.mutate()}
@@ -545,23 +544,21 @@ export default function ChannelPage({
                     </span>
                   </Button>
                 )}
-                {!me.is_demo && (
-                  <IconButton
-                    // Busy blocks the click, not the focus (FocusSafeButton). Nor does a busy toggle
-                    // light up on hover, as if a click would do something.
-                    size="md"
-                    variant={ch?.blocked ? "danger-soft" : "outline-danger"}
-                    onClick={() => block.mutate()}
-                    loading={block.isPending}
-                    label={ch?.blocked ? t("channel.unblock") : t("channel.block")}
-                  >
-                    <Ban />
-                  </IconButton>
-                )}
+                <IconButton
+                  // Busy blocks the click, not the focus (FocusSafeButton). Nor does a busy toggle
+                  // light up on hover, as if a click would do something.
+                  size="md"
+                  variant={ch?.blocked ? "danger-soft" : "outline-danger"}
+                  onClick={() => block.mutate()}
+                  loading={block.isPending}
+                  label={ch?.blocked ? t("channel.unblock") : t("channel.block")}
+                >
+                  <Ban />
+                </IconButton>
                 {/* Hide-from-feed toggle — subscription-scoped, so offered only on a followed channel
                   (mirrors the manager's Eye/EyeOff). Keeps the subscription; only drops its videos
                   from the feed. EyeOff = currently hidden (click to unhide). */}
-                {ch?.subscribed && !me.is_demo && (
+                {ch?.subscribed && (
                   <IconButton
                     size="md"
                     variant={ch.hidden ? "outline-accent" : "outline"}
@@ -573,8 +570,7 @@ export default function ChannelPage({
                     {ch.hidden ? <EyeOff /> : <Eye />}
                   </IconButton>
                 )}
-                {!me.is_demo &&
-                  !ch?.blocked &&
+                {!ch?.blocked &&
                   (ch?.subscribed ? (
                     <Button
                       variant="outline"
@@ -598,7 +594,7 @@ export default function ChannelPage({
                 {/* Tagging is a subscription-scoped action (attach_tag → _user_subscription 404s
                   otherwise), and personal tags are for your subscriptions — so only offer it on a
                   channel you actually follow. */}
-                {ch?.subscribed && !me.is_demo && (
+                {ch?.subscribed && (
                   <div className="min-w-0 flex-1">
                     <ChannelTagsControl
                       userTags={userTags}
@@ -631,7 +627,6 @@ export default function ChannelPage({
                 view={view}
                 setView={setView}
                 canRead={me.can_read}
-                isDemo={me.is_demo}
                 ytSearch={null}
                 onYtSearch={() => {}}
                 onExitYtSearch={() => {}}