feat: add CoreDNS DNS server with UI and WireGuard client integration
DNS:
- Add CoreDNS manager (internal/dns/) with Corefile generation, local zone
records, ad blocklists, and domain allow/block rules - Add /ui/dns settings page and SQLite schema (dns_settings, dns_records,
dns_domain_rules) - Auto-assign link-local client DNS (169.254.20.10) and wire it into
WireGuard client configs; add interface alias routing on Linux/Darwin - Bundle CoreDNS in Docker image; expose port 53 and COREDNS_BIN env
Overview: - Split overview into separate HTMX partials (connections, transfer, server)
- Extend bandwidth snapshot retention to 35 days; enrich chart API with
hourly/daily summaries and peak stats
UI: - Move backup/restore from WireGuard page to /ui/backup
- Add DNS and Backup sidebar items; custom WireGuard icon; users column filter
- Rebuild Tailwind bundle (np-tag-new badge component)