Devcontainer for uv-based monorepo

[ulises-jeremias]

Summary

VS Code/Codespaces devcontainer with uv + Python pin.

CNA mapping

CNA: .devcontainer/devcontainer.json + Dockerfiles.

Acceptance criteria

• devcontainer builds
• Post-create runs uv sync
• Documented in CONTRIBUTING

Blocked by

none

Blocks

none

Reference

Parity matrix (workspace): knowledge/create-python-app-parity-matrix.md
Reference repo: https://github.com/Create-Node-App/create-node-app

Parent epic

#10