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>

mix.exs

@@ -81,7 +81,9 @@ defmodule Berrypod.MixProject do
       {:logger_json, "~> 7.0", only: :prod},
       {:credo, "~> 1.7", only: [:dev, :test], runtime: false},
       {:dialyxir, "~> 1.4", only: [:dev, :test], runtime: false},
-      {:hammer, "~> 7.0"}
+      {:hammer, "~> 7.0"},
+      {:nimble_totp, "~> 1.0"},
+      {:eqrcode, "~> 0.2"}
     ]
   end