feat: merge cartsnitch/api into api/ subdirectory

Consolidate API gateway service into monorepo.
Squashed from https://github.com/cartsnitch/api main (89bacb1).

Co-Authored-By: Paperclip <noreply@paperclip.ing>

Dockerfile

@@ -0,0 +1,26 @@
+FROM python:3.12-slim AS build
+
+RUN apt-get update && apt-get install -y --no-install-recommends \
+    libpq-dev \
+    build-essential \
+    && rm -rf /var/lib/apt/lists/*
+
+WORKDIR /app
+COPY pyproject.toml ./
+COPY src/ ./src/
+RUN pip install --no-cache-dir --prefix=/install .
+
+FROM python:3.12-slim AS prod
+
+WORKDIR /app
+RUN adduser --system --group --uid 1000 app
+COPY --from=build /install /usr/local
+COPY src/ ./src/
+
+USER 1000
+EXPOSE 8000
+
+HEALTHCHECK --interval=30s --timeout=3s \
+    CMD python -c "import urllib.request; urllib.request.urlopen('http://localhost:8000/health')"
+
+CMD ["uvicorn", "cartsnitch_api.main:app", "--host", "0.0.0.0", "--port", "8000"]