feat(pm): add pm-api/pm-frontend services to the ERP stack (serves /pm for the PM panel)

PM joins the ERP traefik (PathPrefix /pm, priority 100), shares the ERP database (additive tables at startup), and reads ERP panels for SSO. PIP_INDEX_URL build arg mirrors the api/bot images.

pm/backend/Dockerfile

@@ -6,7 +6,9 @@ ENV PYTHONDONTWRITEBYTECODE=1 \
     PYTHONUNBUFFERED=1
 
 COPY requirements.txt .
-RUN pip install --no-cache-dir -r requirements.txt
+# PIP_INDEX_URL overridable like the ERP api/bot images (mirror for restricted networks).
+ARG PIP_INDEX_URL=https://pypi.org/simple
+RUN pip install --no-cache-dir -i ${PIP_INDEX_URL} -r requirements.txt
 
 COPY app ./app
 COPY tools ./tools