test: harden collaboration evidence and clean v2 leftovers

[developer-1px]

Summary

• add provider-neutral task-board substitution coverage and a deterministic convergence soak with a scheduled deep profile
• consolidate collaboration checkpoint verification and remove redundant internal helpers and exports
• remove v1-stranded Core code and configuration while preserving the exact v2 public surface
• simplify stale site-route and CI branches

Verification

• npm run verify
• npm run standard:check
• npm run pack:companions
• npm run test:collaboration:soak

The v2 contract remains at one entrypoint, 20 exports, six document members, and zero runtime peers.