Add schedule overlap policy sample

[chaptersix]

Summary

• add a configurable Go Schedule experiment for all six Overlap Policies
• expose the Catchup Window as an optional launcher argument
• log TemporalScheduledStartTime, actual start, and delay from each Workflow
• document expected UI, CLI, Schedule, and Workflow observations with Mermaid diagrams

Validation

• go test ./schedule/overlap/...

Notes

The sample uses a 2-second interval and 5-second Workflow duration so overlap is observable quickly. The README includes a recovery exercise for Catchup Window behavior.