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/index.tsx

@@ -1,18 +1,14 @@
 import type { BunextPageModuleMeta } from "@moduletrace/bunext/types";
 import { SiteData } from "@/src/data/site-data";
-import DashboardHero from "./(sections)/dashboard-hero";
-import DashboardShortcutsSection from "./(sections)/dashboard-shortcuts-section";
 
-export default function AdminDashboardPage() {
-    return (
-        <>
-            <DashboardHero />
-            <DashboardShortcutsSection />
-        </>
-    );
+/**
+ * Never rendered: `index.server.ts` always redirects to `AdminHomePath`.
+ */
+export default function AdminPage() {
+    return null;
 }
 
 export const meta: BunextPageModuleMeta = {
-    title: `Admin Dashboard | ${SiteData["SiteName"]}`,
-    description: `Admin dashboard for managing the ${SiteData["SiteName"]} website.`,
+    title: `${SiteData["SiteName"]}`,
+    description: "Redirecting to your bots.",
 };