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/DiagnosticsSettings.tsx

@@ -7,7 +7,6 @@ import { levelInForce } from "../lib/diagnostics";
 import { focusIsUnclaimed } from "../lib/useFocusKeeper";
 import { updateMeCache, useMe } from "../lib/useMe";
 import { Button } from "./ui/Button";
-import InlineNotice from "./ui/InlineNotice";
 import SegmentedToggle from "./ui/SegmentedToggle";
 import { Section, SettingRow } from "./ui/form";
 import MyLogViewer from "./MyLogViewer";
@@ -99,24 +98,20 @@ export default function DiagnosticsSettings() {
   return (
     <>
       <Section title={t("settings.diagnostics.title")}>
-        {me.is_demo ? (
-          <InlineNotice>{t("settings.diagnostics.demo")}</InlineNotice>
-        ) : (
-          <SettingRow
-            label={t("settings.diagnostics.level")}
-            hint={t("settings.diagnostics.levelHint")}
-          >
-            <div ref={pickerRef}>
-              <SegmentedToggle
-                size="md"
-                ariaLabel={t("settings.diagnostics.level")}
-                value={pending ?? current}
-                onChange={choose}
-                options={LEVELS.map((level) => ({ value: level, label: levelName(level) }))}
-              />
-            </div>
-          </SettingRow>
-        )}
+        <SettingRow
+          label={t("settings.diagnostics.level")}
+          hint={t("settings.diagnostics.levelHint")}
+        >
+          <div ref={pickerRef}>
+            <SegmentedToggle
+              size="md"
+              ariaLabel={t("settings.diagnostics.level")}
+              value={pending ?? current}
+              onChange={choose}
+              options={LEVELS.map((level) => ({ value: level, label: levelName(level) }))}
+            />
+          </div>
+        </SettingRow>
 
         {pending && (
           <div
@@ -186,11 +181,9 @@ export default function DiagnosticsSettings() {
         )}
       </Section>
 
-      {!me.is_demo && (
-        <Section title={t("recorder.settings.title")}>
-          <RecorderSettings />
-        </Section>
-      )}
+      <Section title={t("recorder.settings.title")}>
+        <RecorderSettings />
+      </Section>
 
       <Section title={t("settings.myLog.title")}>
         <MyLogViewer />