Add: Nextcloud Backblaze B2 backup solution - automated daily backups

- Complete backup script for native Nextcloud (MySQL + files)
- Systemd service and timer for daily automated backups at 2 AM
- Backblaze B2 integration with secure credential storage
- Incremental backup support with 30-day retention
- zstd compression for 40-70% storage reduction
- Comprehensive documentation and deployment guides
- Successfully tested with first backup: 203MB DB + 1.3GB files
- Cost-optimized: ~/bin/bash.01-0.02/month for 1.5GB data

Deployment Details:
- Installed B2 CLI via pipx
- Created backup directories at /opt/nextcloud-backup/
- Configured systemd timer for daily execution at 2 AM
- First backup verified in B2 bucket: jg-nextcloud
- Automated scheduling enabled and tested

Documentation includes:
- Deployment report with complete setup details
- Quick start guide for future deployments
- Comprehensive technical reference
- Troubleshooting procedures
- File manifest and index

nextcloud-backup.env.template

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+# Nextcloud Backup Configuration
+# Copy this file to /opt/nextcloud-backup/.env and fill in your values
+
+# ============================================================================
+# NEXTCLOUD CONFIGURATION
+# ============================================================================
+
+# Path to docker-compose directory (where Nextcloud is running)
+# Examples: /opt/nextcloud, /srv/docker/nextcloud, etc.
+NEXTCLOUD_COMPOSE_DIR=/srv/docker/nextcloud
+
+# Full path to Nextcloud data directory
+# This is where user files are stored
+NEXTCLOUD_DATA_PATH=/srv/docker/nextcloud/data
+
+# Database configuration
+# Get these values from your docker-compose.yml or .env file
+NEXTCLOUD_DB_NAME=nextcloud
+NEXTCLOUD_DB_USER=nextcloud
+NEXTCLOUD_DB_PASSWORD=your_database_password_here
+NEXTCLOUD_CONTAINER=nextcloud
+
+# ============================================================================
+# BACKUP CONFIGURATION
+# ============================================================================
+
+# How many days to keep backups
+# Older backups will be automatically deleted
+BACKUP_RETENTION_DAYS=30
+
+# Compression algorithm
+# Options: zstd (recommended, fastest), gzip, bzip2
+COMPRESSION=zstd
+
+# Directory to store local backup metadata and logs
+# Make sure there's enough space for logs
+BACKUP_DIR=/opt/nextcloud-backup/.backups
+
+# Temporary directory for assembling backups before upload
+# Needs enough space for a full database + file archive
+# Typically removed after upload
+TEMP_DIR=/tmp/nextcloud-backup
+
+# ============================================================================
+# BACKUP STRATEGY
+# ============================================================================
+
+# Backup type for scheduled backups
+# Options: incremental (daily, faster) or full (slower, complete snapshot)
+# Default: incremental (recommended)
+BACKUP_TYPE=incremental
+
+# Perform test/dry-run (no actual upload)
+# Set to 'true' for testing, 'false' for actual backups
+DRY_RUN=false
+
+# ============================================================================
+# LOGGING & MONITORING
+# ============================================================================
+
+# Log level: DEBUG, INFO, WARN, ERROR
+LOG_LEVEL=INFO
+
+# Path to log files
+LOG_DIR=${BACKUP_DIR}/logs
+
+# Send alerts on failure (requires mail system configured)
+# Set to your email address to receive failure notifications
+ALERT_EMAIL=admin@example.com
+
+# ============================================================================
+# SCHEDULING (only used by systemd timer)
+# ============================================================================
+
+# Time for daily backup (24-hour format)
+# Examples: 02:00:00 (2 AM), 14:30:00 (2:30 PM)
+BACKUP_TIME=02:00:00
+
+# Optional: Weekly full backup schedule
+# Format: 'Sun' or 'Mon' etc., leave empty for daily incremental only
+FULL_BACKUP_DAY=Sunday