feat: remove register, add evo webhooks, admin view-as user

- Remove /register route and nav links (users created via Evotor webhook)
- Fix evotor_webhooks.py: use phone=None instead of phone="" to avoid unique constraint
- Add admin "view as user" feature: POST /admin/users/{id}/view-as sets viewed_user_id
  in session; POST /admin/view-as/stop clears it
- catalog, vk_catalog, sync, connections GET routes use get_viewed_user() so admins
  see another user's data while browsing
- Orange banner shown at top when admin is viewing as another user

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

web/templates/base.html

@@ -28,7 +28,6 @@
                     <li><a href="/logout" class="secondary">Выход</a></li>
                 {% else %}
                     <li><a href="/login">Вход</a></li>
-                    <li><a href="/register">Регистрация</a></li>
                 {% endif %}
             </ul>
             {% if user %}
@@ -52,13 +51,21 @@
                 <summary role="button" class="outline secondary icon-btn"><i class="bi bi-list"></i></summary>
                 <ul>
                     <li><a href="/login">Вход</a></li>
-                    <li><a href="/register">Регистрация</a></li>
                 </ul>
             </details>
             {% endif %}
         </nav>
     </header>
 
+    {% if viewed_user %}
+    <div style="background:#e65c00;color:#fff;text-align:center;padding:0.4rem 1rem;font-size:0.9rem;">
+        <i class="bi bi-eye me-1"></i>Просмотр от имени: <strong>{{ viewed_user.first_name }} {{ viewed_user.last_name }}</strong> ({{ viewed_user.email }})
+        <form method="post" action="/admin/view-as/stop" style="display:inline;margin-left:1rem;">
+            <button type="submit" style="background:none;border:1px solid #fff;color:#fff;padding:0.1rem 0.6rem;font-size:0.85rem;cursor:pointer;border-radius:4px;">Выйти</button>
+        </form>
+    </div>
+    {% endif %}
+
     <main class="container py-4">
         {% if errors %}
         <div role="alert" class="alert alert-danger">