kv-ffi: report multi-user and open sign-up in server info

Co-Authored-By: Claude Opus 5.5 <[email protected]>

crates/kv-ffi/src/lib.rs

@@ -205,6 +205,10 @@ pub struct ServerInfoDto {
     pub api: u32,
     pub setup_open: bool,
     pub min_client: String,
+    /// The server hosts several accounts, so new ones can join with an invite even after setup.
+    pub multi_user: bool,
+    /// Anyone may create an account here, without an invite.
+    pub open_signup: bool,
 }
 
 #[derive(Debug, Clone, Copy, PartialEq, Eq, uniffi::Enum)]
@@ -763,6 +767,8 @@ impl VaultCore {
             api: info.api,
             setup_open: info.setup_open,
             min_client: info.min_client,
+            multi_user: info.registration.is_some(),
+            open_signup: info.registration == Some(kv_proto::Registration::Open),
         })
     }