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/dict/theme-preferences-dict.ts

@@ -0,0 +1,29 @@
+import { Monitor, Moon, Sun, type LucideIcon } from "lucide-react";
+
+export const ThemePreferences = [
+    {
+        title: "System",
+        value: "system",
+        description: "Follows your device",
+        Icon: Monitor,
+    },
+    {
+        title: "Light",
+        value: "light",
+        description: "Paper and ink",
+        Icon: Sun,
+    },
+    {
+        title: "Dark",
+        value: "dark",
+        description: "Easy at night",
+        Icon: Moon,
+    },
+] as const satisfies {
+    title: string;
+    value: string;
+    description: string;
+    Icon: LucideIcon;
+}[];
+
+export type ThemePreference = (typeof ThemePreferences)[number]["value"];