chore(sdd): bootstrap SDD governance artifacts

[guiribeiro30]

Introduces the Engineering Golden Path SDD governance artifacts for node-vtex-api:

• .specify/memory/constitution.md (v1.0.0) — non-negotiable principles and standards, derived from the node-library family base with adaptations for this repo's "library that embeds a VTEX IO runtime" shape (Koa server, scoped process.env reads via src/constants.ts and src/service/).
• AGENTS.md — agent-facing operational guidance (under 200 lines).
• .gitignore — only .specify/memory/ is tracked; the rest of the spec-kit scaffolding (templates, scripts, integrations) is regeneratable locally via uvx specify init . --here --ai <tool>.

Family detection note: the strict node-library heuristic excludes repos that depend on koa, but the published artifact here is unambiguously a library (main → lib/index.js, typings → lib/index.d.ts, files → ["lib/", "gen/"]). The base was applied with the borderline case documented inline in the constitution.

Generated by the sdd-bootstrap skill (green-field state, public repo).

What is the purpose of this pull request?

What problem is this solving?

How should this be manually tested?

Screenshots or example usage

Types of changes

• Bug fix (a non-breaking change which fixes an issue)
• New feature (a non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)
• Requires change to documentation, which has been updated accordingly.