fix(auth): persist rotated refresh token from tokenrefresh response

[nezumi0627]

Summary

AuthService.tryRefreshToken() discarded the rotated refresh token returned by the server.

RefreshAccessTokenResponse explicitly carries a refreshToken field (packages/types/line_types.ts:13446), and every login path persists the initial one (client/login.ts:110-111, base/login/mod.ts:163-164, 306, 618) — but the refresh path only updated accessToken and expire:

const RATR = await this.refresh({ request: { refreshToken } });
this.client.authToken = RATR.accessToken;
await this.client.storage.set("expire", ...);
// RATR.refreshToken silently dropped

If the server rotates the token (the reason the field exists), the next tryRefreshToken() reuses a stale/invalidated token and dies with a refresh error — permanently breaking long-lived sessions that rely on periodic token refresh.

Fix

Persist RATR.refreshToken when present, before writing expire.

Testing

New mod.test.ts following the existing stub-client pattern (relation/mod.test.ts):

1. Response containing a rotated token → storage now holds "rt-new".
2. Response without rotation → previously stored token is left untouched.

Full suite: deno test --allow-all passes.