Play Framework

chore: add AGENTS.md and bundled OpenSpec skills for Codex

Adds tooling artifacts that complement the existing CLAUDE.md:

- AGENTS.md: Codex-flavoured project overview (build/test commands,
  package map, virtual-thread toggles, testing patterns) so OpenAI's
  Codex agent has the same baseline context Claude reads from CLAUDE.md
- .agents/skills/openspec-*: ten experimental OpenSpec workflow skill
  bundles (explore, new, continue, ff, apply, verify, archive,
  bulk-archive, sync, onboard) -- the same workflow surfaced via the
  /opsx:* slash commands, vendored in-tree so any agent (Claude, Codex,
  etc.) can drive the spec lifecycle without a separate plugin install

Docs/tooling only; no framework code is touched.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>