feat(6): phase 6 plan 02 - operational runbook and documentation

- Created OPERATIONAL_RUNBOOK.md: comprehensive step-by-step procedures for both Docker and Standalone deployment modes covering deployment, daily ops, troubleshooting, backup/restore, disaster recovery, scaling, and updates
- Created HEALTH_MONITORING_CHECKLIST.md: daily/weekly/monthly health check procedures with alert thresholds and quick troubleshooting reference
- Created DISASTER_RECOVERY_PLAN.md: detailed procedures for 6 failure scenarios (database corruption, hardware failure, data center failure, app crash, disk full, network isolation) with RTO/RPO targets
- Created CONFIGURATION_REFERENCE.md: complete documentation of all inventory.env parameters for both deployment modes with common scenarios and troubleshooting
- Created EMERGENCY_PROCEDURES.md: quick-reference incident response playbook with 7 critical scenarios, decision tree, escalation path, and printable cheat sheet
- Created scripts/backup.sh: automated backup script supporting both Docker and Standalone with integrity verification and retention management
- Created scripts/restore.sh: restore script with triple confirmation, safety backups, and validation tests for both deployment modes
- Created config/backup-cron.sh: installer for daily/weekly automated backup cron jobs (2 AM daily, 3 AM Sunday)

All documentation covers dual-deployment modes with shared configuration files.
Documentation is operator-ready with copy-paste commands and clear expected outputs.

backend/Dockerfile

@@ -1,12 +1,19 @@
 FROM python:3.12-slim
 
-# Install system dependencies
+# Metadata labels
+LABEL maintainer="TFM aInventory Team"
+LABEL version="2.0.0"
+LABEL description="TFM aInventory Backend API Service"
+
+# Install system dependencies in single RUN command to reduce layers
 RUN apt-get update && apt-get install -y \
     build-essential \
     libldap2-dev \
     libsasl2-dev \
     gosu \
-    && rm -rf /var/lib/apt/lists/*
+    curl \
+    && rm -rf /var/lib/apt/lists/* \
+    && apt-get clean
 
 WORKDIR /app
 
@@ -35,5 +42,9 @@ RUN chmod +x /app/scripts/init_data.sh /app/backend/entrypoint.sh
 
 EXPOSE 8000
 
+# Health check — verify backend API is responsive
+HEALTHCHECK --interval=30s --timeout=10s --start-period=40s --retries=3 \
+    CMD curl -f http://localhost:8000/health || exit 1
+
 # Entrypoint runs init_data.sh first, then starts uvicorn
 ENTRYPOINT ["/app/backend/entrypoint.sh"]