Port upstream security fixes and features from ngoduykhanh/wireguard-ui

- Escape HTML in client list and wake-on-LAN names to prevent XSS
- Log successful/failed login attempts with remote address
- Fix leading-comma bug in AllowedIPs template when only extra allowed IPs are set
- Add PreUp script support for server interfaces (alongside existing PostUp/PreDown/PostDown)
- Fix endpoint parsing to support IPv6 addresses (upstream PR #223)

Cherry-picked from upstream PRs #656, #653, #680, #673, #223.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

go.sum

@@ -1,5 +1,7 @@
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