fix(webapp): reset the view-as-user flag when switching impersonation target

The flag is scoped to a single impersonation session, which is why stopping
impersonation drops it. Switching straight from one target to another only
became possible in this branch, and that path sets the impersonated id without
touching the flag, so an admin viewing target A as the user landed on target B
with the toggle still on. It is now cleared whenever the target changes.

Author: isshaddad

apps/webapp/app/services/impersonation.server.ts

@@ -45,6 +45,14 @@ export async function getImpersonationId(request: Request) {
 export async function setImpersonationId(userId: string, request: Request) {
   const session = await getImpersonationSession(request);
 
+  // Switching straight to a different target begins a new impersonation session, so the view-as-user
+  // flag must not carry over from the previous one — it's scoped to a single impersonation, which is
+  // why `clearImpersonationId` drops it too. Reachable only since switching stopped requiring a stop
+  // first; before that, every second target arrived via `clearImpersonationId`.
+  if (session.get(IMPERSONATED_USER_ID_KEY) !== userId) {
+    session.unset(VIEWING_AS_USER_KEY);
+  }
+
   session.set(IMPERSONATED_USER_ID_KEY, userId);
 
   return session;