feat(mcp-docugen): scaffold service + Docker stack con gateway Caddy

Task 0 del piano (adattato a workspace uv):
- services/mcp-docugen/: pyproject.toml, src/mcp_docugen/, tests/unit+integration/,
  README, .env.example. Package rinominato da docugen_mcp -> mcp_docugen.
- Root pyproject.toml: aggiunto services/mcp-docugen a workspace members.
- .python-version: 3.11
- uv.lock committato.

Docker stack stile CerberoSuite/Cerbero con prefisso "arca-":
- docker/base.Dockerfile -> arca-base:latest
- docker/mcp-docugen.Dockerfile -> arca-mcp-docugen:dev (porta interna 9100,
  label arca.service, runtime multi-stage, user non-root, healthcheck)
- docker-compose.yml root: gateway Caddy unica porta host (8080) + mcp-docugen
  su rete interna. Security defaults cap_drop ALL, no-new-privileges, read_only
  ove applicabile, restart unless-stopped.
- gateway/Caddyfile: reverse proxy /mcp-docugen/* -> mcp-docugen:9100 + landing.
- gateway/public/index.html: landing page minimale.

.env.example root aggiornato con DOCUGEN_API_KEY + OPENROUTER_API_KEY condivisa.

Task 1-12 (implementazione TDD effettiva) ancora da fare.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

docker/base.Dockerfile

@@ -0,0 +1,13 @@
+FROM python:3.11-slim AS base
+
+RUN apt-get update && apt-get install -y --no-install-recommends \
+    build-essential curl \
+    && rm -rf /var/lib/apt/lists/*
+
+RUN pip install --no-cache-dir "uv>=0.5,<0.7"
+
+WORKDIR /app
+
+COPY pyproject.toml uv.lock* ./
+
+ENV PATH="/app/.venv/bin:$PATH"

docker/mcp-docugen.Dockerfile

@@ -0,0 +1,26 @@
+ARG BASE_TAG=latest
+
+FROM arca-base:${BASE_TAG} AS builder
+COPY services/mcp-docugen ./services/mcp-docugen
+RUN uv sync --frozen --no-dev --package mcp-docugen
+
+FROM python:3.11-slim AS runtime
+LABEL org.opencontainers.image.source="https://git.tielogic.xyz/Adriano/ArcaSuite" \
+      arca.service="mcp-docugen"
+
+WORKDIR /app
+COPY --from=builder /app /app
+ENV PATH="/app/.venv/bin:$PATH"
+
+RUN useradd -m -u 1000 app && \
+    mkdir -p /data && chown app:app /data
+USER app
+VOLUME ["/data"]
+
+ENV HOST=0.0.0.0 PORT=9100 DATA_DIR=/data
+EXPOSE 9100
+
+HEALTHCHECK --interval=30s --timeout=5s --retries=3 --start-period=15s \
+    CMD python -c "import httpx, os; httpx.get(f'http://localhost:{os.environ.get(\"PORT\",\"9100\")}/health').raise_for_status()"
+
+CMD ["mcp-docugen"]