Make Cobble a local install: setup flow, bots-first admin, settings

Local, password-only auth:
- No public pages; everything outside /admin and /auth redirects in
- First run (no users) sends every page to /auth/signup, which creates
  the super admin (user #1) once and then locks
- Login is email/username + password; removed the emailed-code flow,
  /auth/sso and email password reset
- Google login kept for existing accounts only, never creates them
- seed-super-admin now requires SEED_SUPER_ADMIN_PASSWORD

Bots-first admin:
- /admin and closed sections (people, logs, backups) redirect to
  /admin/bots; only bots and settings are live (AdminSections)
- Removed the old admin layout; every /admin page uses the bots rail
- Coordinator bot created at signup/seed and by /admin/bots
  (ensureCoordinatorBot), which redirects to its chat
- bots.system_prompt (markdown) with a default coordinator prompt
- seed-bots reuses the existing coordinator

Settings:
- Sub pages general (default), profile, change-password, listed in the
  rail with a back link; unknown settings paths redirect to general
- Redesigned settings UI: pane header, grouped rows, sticky save bar
- General: System/Light/Dark theme, saved per device

Co-Authored-By: Claude Opus 5.5 <[email protected]>

src/pages/admin/settings/(partials)/settings-group.tsx

@@ -0,0 +1,34 @@
+import type { ReactNode } from "react";
+import Stack from "@moduletrace/twui/layout/Stack";
+import H2 from "@moduletrace/twui/layout/H2";
+import Span from "@moduletrace/twui/layout/Span";
+
+type Props = {
+    title: string;
+    description?: ReactNode;
+    children: ReactNode;
+};
+
+/**
+ * One block of settings: what it is on the left, the controls on the right.
+ * Stacks below 768px. Blocks are separated by hairlines, never cards.
+ */
+export default function SettingsGroup({ title, description, children }: Props) {
+    return (
+        <Stack className="w-full gap-4! md:grid md:grid-cols-[200px_1fr] md:gap-10! py-8 border-0 border-b border-solid border-hairline last:border-b-0">
+            <Stack className="gap-1! min-w-0">
+                <H2 className="text-sm! leading-5! tracking-normal! font-bold text-ink mb-0!">
+                    {title}
+                </H2>
+                {description ? (
+                    <Span className="text-[13px] leading-[18px] text-ink-secondary">
+                        {description}
+                    </Span>
+                ) : null}
+            </Stack>
+            <Stack className="gap-4! min-w-0 w-full items-stretch">
+                {children}
+            </Stack>
+        </Stack>
+    );
+}