feat(ci): add devcontainer and copilot workflow docs

[icornett]

Summary

• add a production-ready devcontainer setup and validation workflow
• add repository-level Copilot instructions aligned with CLAUDE.md guidance
• add repository memory bank structure and ADRs for project foundation and devcontainer architecture
• add pre-commit configuration and update golangci-lint hook to use local v2-compatible CLI (--fast-only)
• apply formatting fixes from pre-commit hooks across docs/config files

Notes

• branch is hosted in fork and proposed to upstream via cross-repo PR
• all pre-commit hooks pass locally