chore: add Docker deployment setup and health check wiring

- Add multi-stage Dockerfile for backend (SDK build → ASP.NET runtime,
  non-root user, /health HEALTHCHECK)
- Add docker-compose.dev.yml orchestrating extrudex-api + control-center-web
- Add deploy.sh convenience script wrapping docker compose up --build
- Wire ASP.NET health checks: AddHealthChecks().AddNpgSql() + MapHealthChecks("/health")
- Add backend .dockerignore (comprehensive pattern list)
- Exclude frontend/dist, frontend/node_modules, frontend/.angular from git

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

backend/Dockerfile

@@ -0,0 +1,34 @@
+# ── Stage 1: Build ──────────────────────────────────────────
+FROM mcr.microsoft.com/dotnet/sdk:9.0 AS build
+WORKDIR /src
+
+# Copy csproj first for layer caching — restores before copying source
+COPY Extrudex.csproj .
+RUN dotnet restore
+
+# Copy the rest of the source
+COPY . .
+RUN dotnet publish Extrudex.csproj \
+    -c Release \
+    -o /app/publish \
+    --no-restore
+
+# ── Stage 2: Runtime ────────────────────────────────────────
+FROM mcr.microsoft.com/dotnet/aspnet:9.0 AS runtime
+WORKDIR /app
+
+# Non-root user for security
+RUN adduser --disabled-password --gecos "" appuser
+USER appuser
+
+# Copy published output from build stage
+COPY --from=build /app/publish .
+
+# ASP.NET Core listens on 8080 by default in .NET 8+
+EXPOSE 8080
+
+# Health check against /health endpoint
+HEALTHCHECK --interval=30s --timeout=5s --start-period=10s --retries=3 \
+    CMD curl --fail http://localhost:8080/health || exit 1
+
+ENTRYPOINT ["dotnet", "Extrudex.dll"]