[SIMPL-30451] Add distributed-execution service with guide and reference implementations

Canonical location for documentation, example workflows and reference service implementations covering distributed execution patterns. Covers AC1-AC4: execution-target selection, decision support, readiness checks and code-level linkage. Tightly coupled jobs and the loosely coupled subprocess transport are verified by the test suite; the Kubernetes pipes transport is implemented but not yet cluster-run and is marked as such in the guide.

Changelog: added

Dockerfile

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+FROM python:3.12-slim-bookworm
+
+COPY --from=ghcr.io/astral-sh/uv:0.10.8 /uv /uvx /bin/
+
+RUN python -m pip install --no-cache-dir --upgrade "pip==26.1.2"
+
+WORKDIR /app
+
+# Explicit UID 1000 matches the runtime UID expected by the Dagster chart
+RUN addgroup --gid 1000 appgroup && \
+    adduser --uid 1000 --gid 1000 --disabled-password --gecos "" appuser
+
+RUN apt-get update && apt-get upgrade -y \
+    && apt-get install -y --no-install-recommends \
+    git=1:2.39.5-0+deb12u3 \
+    curl=7.88.1-10+deb12u15 \
+    && apt-get clean \
+    && rm -rf /var/lib/apt/lists/* /tmp/* /var/tmp/*
+
+RUN chown -R appuser:appgroup /app /opt
+
+COPY pyproject.toml .
+COPY uv.lock .
+COPY src/ ./src/
+COPY payload/ ./payload/
+COPY workspace.yaml .
+
+ENV UV_COMPILE_BYTECODE=1
+ENV UV_LINK_MODE=copy
+
+RUN --mount=type=cache,target=/root/.cache/uv \
+    uv sync --locked --no-dev
+
+ENV PATH="/app/.venv/bin:${PATH}"
+ENV PYTHONPATH="/app/src"
+
+USER appuser
+
+RUN dagster --version
+
+EXPOSE 4000
+
+CMD ["dagster", "code-server", "start", "-h", "0.0.0.0", "-p", "4000", "-f", "src/distributed_execution/repository.py"]