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/sync.py

@@ -5,7 +5,7 @@ from fastapi import APIRouter, Depends, Request
 from fastapi.responses import 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 SyncConfig
@@ -23,13 +23,14 @@ def _render(request: Request, ctx: dict):
 @router.get("/sync")
 async def sync_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)
 
-    config = db.query(SyncConfig).filter_by(user_id=user.id).first()
+    config = db.query(SyncConfig).filter_by(user_id=viewed_user.id).first()
     return _render(request, {
-        "user": user,
+        "user": real_user,
+        "viewed_user": viewed_user if viewed_user.id != real_user.id else None,
         "config": config,
         "saved": request.query_params.get("saved"),
     })