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/ui/Banner.tsx

@@ -20,7 +20,7 @@ const TONES: Record<BannerTone, { bar: string; icon: string; action: "primary" |
   },
 };
 
-// Shared top-of-app notification bar. VersionBanner and DemoBanner are thin wrappers over this;
+// Shared top-of-app notification bar. VersionBanner and VerifyBanner are thin wrappers over this;
 // a future news-ticker variant can build on the same shell (rotating content as children).
 export default function Banner({
   tone,
@@ -41,7 +41,7 @@ export default function Banner({
    *  control is not an acceptable default, and `Button`'s type now says so. */
   dismissTitle?: string;
   /** `"status"` for a bar that APPEARS in response to something the user just did, so a screen
-   * reader announces it. Left unset for the permanent bars (demo, version): those are part of the
+   * reader announces it. Left unset for the permanent bars (version): those are part of the
    * page when it loads, and announcing them on every visit is noise, not information. */
   role?: "status";
 }) {

frontend/src/components/ui/PageShell.tsx

@@ -41,7 +41,7 @@ export function PageToolbar({ children }: { children: ReactNode }) {
 //  - `title`   — the page's name as a visually hidden `h1` (B4): the nav rail and the tab title are
 //                the visible identity, and a screen reader still lands on a named page. A view that
 //                shows its own title renders it through `PageHeading`, and this one steps aside.
-//  - `banners` — in-flow, fixed notices (demo/version) above the scroll region.
+//  - `banners` — in-flow, fixed notices (verify/version) above the scroll region.
 //  - toolbar band — in-flow, FIXED per-module band (filter chips / sort / counts); filled by a
 //                module via <PageToolbar>. Empty ⇒ zero height, so pages without one lose nothing.
 //  - children  — the ONE scrollable region. `PageScroller` owns the scroller and its two