Add Codespaces development environment

[krowvin]

Summary

• add a reproducible GitHub Codespaces development container for the Batch Events API and UI
• install Python 3.12 dependencies, Node.js 22, locked UI dependencies, and Docker Compose with an isolated Docker daemon
• prepare the external cwms Docker network required by the local Compose stack
• configure forwarded ports and editor tooling for Python, TypeScript, ESLint, and Docker
• document Codespaces setup, verification, service startup, and credential boundaries
• ignore TypeScript build metadata generated by the documented UI build

Why

Developers currently need to install and align Python, Node.js, Docker, project dependencies, UI dependencies, and the local Docker network manually. The development container makes a new self-hosted Codespace ready for tests and local full-stack development while retaining mock authentication and local-only service credentials by default.

Validation

• Dev Container image build succeeded
• Dev Container lifecycle startup and post-create setup succeeded
• python -m pytest -q — 111 passed, 1 existing dependency deprecation warning
• npm --prefix ui run lint — passed
• npm --prefix ui run build — passed with existing asset-resolution and chunk-size warnings
• docker compose config --quiet — passed
• docker compose up --detach --build — built and started the API, dispatcher, PostgreSQL, MinIO, Flyway, and ElasticMQ
• PostgreSQL reported healthy and GET /health returned {status:ok}