fix: preserve user token namespace on refresh

[dajiaohuang]

Why

UserAccessToken.get(key, { namespace }) reads from the requested namespace, but both successful recovery paths wrote the refreshed token without forwarding that namespace. The custom namespace stayed expired, so subsequent reads refreshed again and the new token was stored under the app-ID namespace.

What changed

• Forward the requested namespace when persisting refresh-token results.
• Forward it for the authorization-code fallback as well.
• Add regression tests proving two reads from a custom namespace perform only one refresh/code exchange.

Validation

• corepack yarn test --runInBand client/__tests__/user-access-token.test.ts — 2 passed
• corepack yarn test --runInBand — 47 suites passed; 447 passed, 5 skipped
• git diff --check

Closes #210