Containerize InfraForge backend runtime for reproducible Azure deployment

[Copilot]

InfraForge had no backend container definition, which made Azure deployment non-reproducible and left runtime dependencies implicit. This change adds a first-class container runtime for the FastAPI app, including SQL Server ODBC support and a documented smoke-test path for the health endpoint.

• Runtime image

  • Adds a Python 3.13 Dockerfile for the backend runtime.
  • Installs required Linux system packages plus Microsoft ODBC Driver 18 for SQL Server.
  • Uses the existing app entrypoint (python web_start.py) so container startup matches the supported runtime path.

• Deterministic build context

  • Adds .dockerignore to exclude local state, repo metadata, large non-runtime assets, and test/docs content from the image build context.

• Startup compatibility

  • Updates the Copilot SDK type import in src/copilot_helpers.py to use copilot.session, which matches the installed SDK and keeps app startup/imports working in the containerized runtime.

• Health smoke-test coverage

  • Adds a focused health endpoint test for /api/health?check=sql.
  • Documents a lightweight container smoke-test command that serves the app with FastAPI lifespan hooks disabled so endpoint reachability can be verified without Azure-backed startup dependencies.

• Runbook updates

  • Extends DEMO_GUIDE.md with:
    • local image build
    • full container run with .env
    • health endpoint smoke-test flow
    • image push pattern for Azure-hosted container deployment

FROM python:3.13-slim

RUN apt-get update \
    && apt-get install -y --no-install-recommends unixodbc lsof \
    && ACCEPT_EULA=Y apt-get install -y --no-install-recommends msodbcsql18

CMD ["python", "web_start.py"]