separate account settings from shop settings

- Create dedicated /admin/account page for user account management
- Move email, password, and 2FA settings from /admin/settings
- Add Account link to top of admin sidebar navigation
- Add TOTP-based two-factor authentication with NimbleTOTP
- Add TOTP verification LiveView for login flow
- Add AccountController for TOTP session management
- Remove Advanced section from settings (duplicated in dev tools)
- Remove user email from sidebar footer (replaced by Account link)

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

lib/berrypod_web/components/layouts/admin.html.heex

@@ -34,6 +34,19 @@
     <aside class="admin-sidebar">
       <%!-- nav links --%>
       <nav class="admin-sidebar-nav" aria-label="Admin navigation">
+        <div class="admin-nav-group">
+          <ul class="admin-nav">
+            <li>
+              <.link
+                navigate={~p"/admin/account"}
+                class={admin_nav_active?(@current_path, "/admin/account")}
+              >
+                <.icon name="hero-user-circle" class="size-5" /> Account
+              </.link>
+            </li>
+          </ul>
+        </div>
+
         <div class="admin-nav-group">
           <span class="admin-nav-heading">Shop</span>
           <ul class="admin-nav">
@@ -174,9 +187,6 @@
       <%!-- sidebar footer --%>
       <div class="admin-sidebar-footer">
         <ul class="admin-nav">
-          <li class="admin-sidebar-email truncate">
-            <.icon name="hero-user" class="size-5" /> {@current_scope.user.email}
-          </li>
           <li>
             <details class="admin-dev-tools">
               <summary>