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/components/general/theme-init-script.tsx

@@ -1,3 +1,5 @@
+import { AppData } from "@/src/data/app-data";
+
 /**
  * Applies the saved color scheme to `<html>` before first paint, so pages
  * never flash light before twui's `ColorSchemeSelector` mounts. Mirrors the
@@ -5,7 +7,7 @@
  */
 const ThemeInitScriptSource = `(function () {
     try {
-        var theme = localStorage.getItem("theme");
+        var theme = localStorage.getItem("${AppData["ThemeStorageKey"]}");
         if (theme !== "dark" && theme !== "light") {
             theme = window.matchMedia("(prefers-color-scheme: dark)").matches
                 ? "dark"