One read of a device's link: state::credentials, with the client's seal

Five places read the server address and token straight from sync_state:
sharing, autosync, sync_unlink, update's download token, and the ffi. Reading it
raw is how Android came to send its sealed token to the share routes (#5381).
state::credentials(conn, seal) now holds that read. With a seal it opens the token
(open_token), and without one (the desktop keeps it plain) it returns it as stored.
Every site calls it.

DRY pass #2, batch 1, F1 (#5372).

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

android/ffi/src/lib.rs

@@ -753,14 +753,8 @@ impl Inkwell {
     /// it (`state::open_token`), so the app asks to sign in again.
     fn credentials(&self) -> Result<(String, String), CoreError> {
         let conn = self.db.conn().map_err(CoreError::store)?;
-        let current = state::read(&conn).map_err(CoreError::store)?;
-        let (Some(url), Some(stored)) = (current.server_url, current.device_token) else {
-            return Err(CoreError::NotLinked);
-        };
-        match state::open_token(&conn, &stored, &self.seal).map_err(CoreError::store)? {
-            Some(token) => Ok((url, token)),
-            None => Err(CoreError::NotLinked),
-        }
+        let link = state::credentials(&conn, Some(&self.seal)).map_err(CoreError::store)?;
+        link.ok_or(CoreError::NotLinked)
     }
 
     /// Persist a fresh link, adopting the server's retention window at the same time