feat(ipv6): add IPv6 support for Cloudflare ranges

[somethingwithproof]

Description

Add IPv6 support for Cloudflare IP range synchronization with UFW.

Motivation

• Cloudflare serves significant traffic over IPv6
• Complete firewall coverage requires both IP versions
• Modern infrastructure increasingly IPv6-first

Proposed Solution

1. Fetch IPv6 ranges from Cloudflare API
2. Add UFW rules for IPv6 addresses
3. Handle dual-stack configuration
4. Add IPv6-specific validation

Acceptance Criteria

• Fetch Cloudflare IPv6 ranges
• Create UFW rules for IPv6
• Validate IPv6 address format
• Handle IPv6 CIDR notation
• Update documentation

API Endpoints

# IPv4
https://www.cloudflare.com/ips-v4

# IPv6
https://www.cloudflare.com/ips-v6

Commits should follow

feat(ipv6): add IPv6 range fetching
feat(ufw): implement IPv6 rule creation
test: add IPv6 validation tests