Always send initOrganization and orgUserHasExistingUser in org invite URL (#7482)

The bundled web vault (2026.6.4) requires seven query parameters in the
accept-organization URL and rejects the invite client-side when any of them is
null, showing only "Unable to accept invitation" without sending a request to
the server.

send_invite() never appended initOrganization, and appended
orgUserHasExistingUser only for users who already had an account, so every
organization invitation e-mail produced a link that could not be accepted.

Web vault 2026.4.1 (shipped with 1.36.0) read these parameters null-safely,
which is why this only appeared in 1.37.0.

Fixes #7481

Co-authored-by: Claude Opus 5 <noreply@anthropic.com>

src/mail.rs

@@ -307,9 +307,18 @@ pub async fn send_invite(
         if CONFIG.sso_enabled() && CONFIG.sso_only() {
             query_params.append_pair("orgSsoIdentifier", &org_id);
         }
-        if user.private_key.is_some() {
-            query_params.append_pair("orgUserHasExistingUser", "true");
-        }
+
+        // The web vault requires both of these parameters to be present.
+        // If either is missing it rejects the invite client-side, before any
+        // request reaches the server, showing only "Unable to accept invitation".
+        query_params.append_pair("initOrganization", "false");
+
+        let org_user_has_existing_user = if user.private_key.is_some() {
+            "true"
+        } else {
+            "false"
+        };
+        query_params.append_pair("orgUserHasExistingUser", org_user_has_existing_user);
     }
 
     let Some(query_string) = query.query() else {