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.

infrastructure/postfix/TrustedHosts

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+# OpenDKIM Trusted Hosts
+# These hosts are allowed to send mail through this server
+
+# Localhost
+127.0.0.1
+localhost
+
+# Docker networks (adjust based on your Docker setup)
+172.17.0.0/16
+172.18.0.0/16
+172.19.0.0/16

infrastructure/postfix/main.cf

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+# Postfix main configuration for DocFast
+# Minimal SMTP relay for application email sending
+
+# Basic configuration
+smtpd_banner = $myhostname ESMTP
+biff = no
+append_dot_mydomain = no
+readme_directory = no
+compatibility_level = 3.6
+
+# Network configuration
+myhostname = docfast.dev
+mydomain = docfast.dev
+myorigin = docfast.dev
+inet_interfaces = 127.0.0.1, 172.17.0.1  # localhost + Docker bridge
+inet_protocols = ipv4
+mydestination =  # Empty = relay only, no local delivery
+mynetworks = 127.0.0.0/8, 172.17.0.0/16, 172.18.0.0/16
+
+# TLS configuration
+smtp_tls_security_level = may
+smtp_tls_CAfile = /etc/ssl/certs/ca-certificates.crt
+
+# OpenDKIM integration
+milter_protocol = 6
+milter_default_action = accept
+smtpd_milters = inet:localhost:8891
+non_smtpd_milters = $smtpd_milters
+
+# Size limits
+mailbox_size_limit = 0
+message_size_limit = 10240000  # 10MB
+
+# Other settings
+recipient_delimiter = +
+disable_vrfy_command = yes
+smtpd_helo_required = yes
+
+# Rate limiting
+smtpd_client_connection_count_limit = 10
+smtpd_client_connection_rate_limit = 10
+
+# Logging
+maillog_file = /var/log/postfix.log

infrastructure/postfix/opendkim.conf

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+# OpenDKIM Configuration for DocFast
+
+# Logging
+Syslog yes
+SyslogSuccess yes
+LogWhy yes
+
+# Operating mode (s = sign, v = verify, sv = both)
+Mode sv
+
+# Canonicalization
+Canonicalization relaxed/simple
+
+# Domain and selector
+Domain docfast.dev
+Selector mail
+KeyFile /etc/opendkim/keys/docfast.dev/mail.private
+
+# Network
+Socket inet:8891@localhost
+PidFile /run/opendkim/opendkim.pid
+
+# Security
+OversignHeaders From
+TrustAnchorFile /usr/share/dns/root.key
+UserID opendkim
+
+# Trusted hosts (who can send mail through this server)
+InternalHosts /etc/opendkim/TrustedHosts
+ExternalIgnoreList /etc/opendkim/TrustedHosts
+
+# Additional security options
+RequireSafeKeys yes
+SendReports yes
+ReportAddress "postmaster@docfast.dev"
+
+# Performance
+MaximumHeaders 30