Add infrastructure for contributors to optionally use OpenSpec for AI-assisted development with structured proposal/design/spec workflows. Directory structure separates tracked content from local tooling: - doc/specs/ - Main specs (source of truth, tracked) - doc/context/ - Shared context files like language change checklist (tracked) - openspec/ - Workflow state and config (local only, gitignored) Setup script (_scripts/setup-openspec.sh): - Creates openspec/config.yaml pointing to doc/specs - Runs 'openspec init' to generate AI agent skills - Supports 'update' mode for regenerating after OpenSpec upgrades Updated .gitignore to exclude local-only tooling: - openspec/, .cursor/ - AI agent skills in .claude/, .codex/, .gemini/, .github/ Updated CONTRIBUTING.md with setup instructions for contributors. Signed-off-by: Marcel van Lohuizen <mpvl@gmail.com> Change-Id: I1a2cae18d34922ecde8828a546bc30fb89ac5bf8 Reviewed-on: https://cue.gerrithub.io/c/cue-lang/cue/+/1231007 TryBot-Result: CUEcueckoo <cueckoo@cuelang.org> Reviewed-by: Daniel Martí <mvdan@mvdan.cc> Unity-Result: CUE porcuepine <cue.porcuepine@gmail.com>