Integration tests failing on demo API

[github-actions]

The nightly integration test run failed.

• Workflow: Integration tests (demo API, nightly)
• Run: https://github.com/TexasCoding/kalshi-python-sdk/actions/runs/25991928222
• Commit: dafa1fb8097dba2a6650b7ab24aa9a2e8243e941
• Triggered by: workflow_dispatch

See the run logs above for the failing tests. This issue is reused across nightly runs;
close it once the integration suite is green again.

[TexasCoding]

Duplicate of #124 (which already tracks the 11 currently-failing integration tests + the nightly silent-no-op pattern). The integration-nightly workflow's failure-reporting step is what auto-opened this — worth adding fingerprint-style dedup to that step (mirror what spec-sync.yml does) so it stops opening a new issue every night. Tracked under #124.