feat(workshop): publish Polymarket learner artifacts

[sishuo-yang]

Summary

• publish the Polymarket collector, ClickHouse schema and queries, Docker Compose configuration, environment template, preflight, and tests under workshop_public/polymarket
• add a public README that directs learners to the hosted WorkshopHouse playbook
• make the ClickHouse integration test self-contained within the public package
• update workshop CI to trigger on and test the new public location on Linux and Windows

Companion playbook

• ClickHouse/WorkshopHouse#11

The playbook now directs learners to ClickHouse_Demos/workshop_public/polymarket. This PR should land before the WorkshopHouse change is promoted to production.

Validation

• collector unit suite: 49 passed, 1 optional integration test skipped
• disposable ClickHouse 26.3 integration: passed
• shell syntax validation: passed
• Docker Compose configuration validation: passed
• workflow YAML parse: passed