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/routes/connections.py

@@ -8,7 +8,7 @@ from fastapi import APIRouter, Depends, Request
 from fastapi.responses import HTMLResponse, JSONResponse, RedirectResponse
 from sqlalchemy.orm import Session
 
-from web.auth.session import get_current_user
+from web.auth.session import get_current_user, get_viewed_user
 from web.config import settings
 from web.database import get_db
 from web.models.connections import EvotorConnection, VkConnection
@@ -32,13 +32,18 @@ def _now() -> datetime:
 @router.get("/connections")
 async def connections_get(request: Request, db: Session = Depends(get_db)):
     try:
-        user = get_current_user(request, db)
+        real_user, viewed_user = get_viewed_user(request, db)
     except Exception:
         return RedirectResponse("/login", 303)
 
-    evotor = db.query(EvotorConnection).filter_by(user_id=user.id).first()
-    vk = db.query(VkConnection).filter_by(user_id=user.id).first()
-    return _render(request, "connections.html", {"user": user, "evotor": evotor, "vk": vk})
+    evotor = db.query(EvotorConnection).filter_by(user_id=viewed_user.id).first()
+    vk = db.query(VkConnection).filter_by(user_id=viewed_user.id).first()
+    return _render(request, "connections.html", {
+        "user": real_user,
+        "viewed_user": viewed_user if viewed_user.id != real_user.id else None,
+        "evotor": evotor,
+        "vk": vk,
+    })
 
 
 @router.post("/connections/evotor")