Add complete infrastructure automation and documentation

- infrastructure/setup.sh: Master provisioning script for fresh Ubuntu servers
- infrastructure/docker-compose.yml: Production Docker Compose configuration
- infrastructure/.env.template: Environment variables template
- infrastructure/nginx/: Nginx configuration with security headers
- infrastructure/postfix/: Postfix + OpenDKIM email configuration
- infrastructure/README.md: Complete disaster recovery guide
- scripts/docfast-backup.sh: SQLite backup script with rotation

All services now fully reproducible with documented disaster recovery procedures.

scripts/docfast-backup.sh

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+#!/bin/bash
+# DocFast SQLite Backup Script
+# Runs every 6 hours via cron. Keeps 7 daily + 4 weekly backups.
+
+set -euo pipefail
+
+BACKUP_DIR="/opt/docfast-backups"
+DB_PATH="/var/lib/docker/volumes/docfast_docfast-data/_data/docfast.db"
+DATE=$(date +%Y-%m-%d_%H%M)
+DAY_OF_WEEK=$(date +%u)  # 1=Monday, 7=Sunday
+
+mkdir -p "$BACKUP_DIR"
+
+# Check if database exists
+if [[ ! -f "$DB_PATH" ]]; then
+    echo "ERROR: Database not found at $DB_PATH" >&2
+    exit 1
+fi
+
+# Safe hot backup using sqlite3 .backup
+DAILY_FILE="$BACKUP_DIR/docfast-daily-${DATE}.db"
+sqlite3 "$DB_PATH" ".backup '$DAILY_FILE'"
+
+# Verify backup is valid
+if ! sqlite3 "$DAILY_FILE" "PRAGMA integrity_check;" | grep -q "^ok$"; then
+    echo "ERROR: Backup integrity check failed!" >&2
+    rm -f "$DAILY_FILE"
+    exit 1
+fi
+
+echo "Created backup: $DAILY_FILE ($(stat -c%s "$DAILY_FILE") bytes)"
+
+# On Sundays, also keep a weekly copy
+if [ "$DAY_OF_WEEK" -eq 7 ]; then
+    WEEKLY_FILE="$BACKUP_DIR/docfast-weekly-$(date +%Y-%m-%d).db"
+    cp "$DAILY_FILE" "$WEEKLY_FILE"
+    echo "Created weekly backup: $WEEKLY_FILE"
+fi
+
+# Rotate: keep last 7 daily backups (28 files at 6h intervals = ~7 days)
+find "$BACKUP_DIR" -name "docfast-daily-*.db" -type f | sort -r | tail -n +29 | xargs -r rm -f
+
+# Rotate: keep last 4 weekly backups
+find "$BACKUP_DIR" -name "docfast-weekly-*.db" -type f | sort -r | tail -n +5 | xargs -r rm -f || true
+
+# Show current backup status
+DAILY_COUNT=$(find "$BACKUP_DIR" -name "docfast-daily-*.db" -type f | wc -l)
+WEEKLY_COUNT=$(find "$BACKUP_DIR" -name "docfast-weekly-*.db" -type f | wc -l)
+echo "Backup rotation complete. Daily: $DAILY_COUNT, Weekly: $WEEKLY_COUNT"