docs(agents): archive full-playability programme plan

[blakinio]

Purpose

Archive the completed OTC2-20260801-full-playability-program-plan lifecycle after planning PR #135 merged as 72a45210aafd682d6d9e95c54c1fee55dca46abb.

Scope

• add the completed record under docs/agents/tasks/archive/;
• remove the corresponding record from docs/agents/tasks/active/;
• preserve exact validation evidence and the single next action for P0 launch.

Safety

• exactly two lifecycle paths;
• no programme document, prompt, source, manifest, lockfile or workflow change;
• no implementation authorization.

Next gate

After this archive merges, run a fresh P0 coordinator launch preflight against exact current main and create five isolated docs/evidence-only discovery tasks, branches and draft PRs.