Add a token refresh example for auth.refreshToken

[TDanks2000]

Background

The wrapper supports OAuth authorization-code flow, device-code flow, and token refresh. The README and examples show sign-in flows, but a short refresh-token example would help apps keep Trakt sessions alive without making users sign in again.

Proposed change

Add a concise example showing trakt.auth.refreshToken and trakt.setAccessToken, with a note that apps should persist the returned refresh token securely.

Acceptance criteria

• docs/examples.md includes a token refresh example.
• The example uses the existing auth.refreshToken method.
• The wording does not recommend storing tokens in client-side source code.
• bun run verify passes.

Files likely involved

• docs/examples.md
• README.md