Remove edge case and out-of-scope test files

Keep only core feature tests:
- single-open-invariant.spec.ts (single-open safety)
- nested-delegation-resume.spec.ts (automatic parent resume)
- delegation-events.spec.ts (lifecycle events)
- history-resume-delegation.spec.ts (history resume)
- new-task-delegation.spec.ts (new_task tool)
- provider-delegation.spec.ts (provider delegation)

Remove edge case tests to keep PR focused on core functionality.

Author: hannesrudolph