Add new features and enhancements to CI workflows and backend.

Enhanced CI workflows by adding an Alpine-based smoke test for the backend with PostgreSQL 16. Updated the Docker build process to support dynamic base images and added provenance, SBOM, and labels to Docker builds. Extended branch compatibility checks and refined backend configurations for broader usage scenarios.

backend/Dockerfile

@@ -1,4 +1,5 @@
-FROM python:3.13-slim AS base
+ARG PYTHON_BASE_IMAGE=python:3.13-slim
+FROM ${PYTHON_BASE_IMAGE} AS base
 
 ENV PYTHONDONTWRITEBYTECODE=1
 ENV PYTHONUNBUFFERED=1
@@ -6,11 +7,17 @@ ENV PIP_NO_CACHE_DIR=1
 
 WORKDIR /app
 
-RUN apt-get update \
-    && apt-get upgrade -y \
-    && rm -rf /var/lib/apt/lists/*
+RUN if command -v apt-get >/dev/null 2>&1; then \
+      apt-get update && apt-get upgrade -y && rm -rf /var/lib/apt/lists/*; \
+    elif command -v apk >/dev/null 2>&1; then \
+      apk upgrade --no-cache; \
+    fi
 
-RUN addgroup --system app && adduser --system --ingroup app app
+RUN if addgroup --help 2>&1 | grep -q -- '--system'; then \
+      addgroup --system app && adduser --system --ingroup app app; \
+    else \
+      addgroup -S app && adduser -S -G app app; \
+    fi
 
 COPY requirements.txt /app/requirements.txt
 RUN pip install --upgrade pip && pip install -r /app/requirements.txt