fix(webapp): say single sign-on in the email modal, not identity provider

"Signs you in through its own identity provider" led with the jargon. Single
sign-on is the term someone will have been given by whoever set it up, so the
sentence now opens with that and leaves the identity provider as the place the
address actually lives.

"An admin on your account" was also ambiguous - it's an organization admin, and
"your account" could be read as the reader's own.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>

Author: samejr

apps/webapp/app/routes/account._index/route.tsx

@@ -586,9 +586,9 @@ function EditEmailButton({ isSsoManaged }: { isSsoManaged: boolean }) {
           </DialogHeader>
           {isSsoManaged ? (
             <Paragraph variant="small" className="py-4">
-              Your organization signs you in through its own identity provider, so your email
-              address is managed there rather than here. To change it, ask an admin on your account
-              to update it for you.
+              Your organization uses single sign-on, so your email address is managed by your
+              identity provider rather than here. To change it, ask an organization admin to update
+              it for you.
             </Paragraph>
           ) : (
             <fetcher.Form method="post">