Replace from-scratch rewrite with real ngoduykhanh/wireguard-ui fork

The from-scratch Go rewrite had unresolved bugs (missing go.sum, UI
404s, path issues) from being built without a working local Go
toolchain to verify against. Switching strategy: use the actual
upstream wireguard-ui codebase (proven, battle-tested single-server
manager) as the base, and extend it for multi-server support instead
of re-deriving everything from zero.

Kept our own installers (bootstrap.sh, update.sh, scripts/install.sh,
scripts/proxmox-install.sh) - these still apply, just need updating
to build/install the upstream module layout instead of the old
cmd/wireguard-ui-multi structure.

Module path intentionally left as upstream's own
(github.com/ngoduykhanh/wireguard-ui) for now to avoid touching every
internal import; revisit if this needs to be fully rebranded.

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

router/validator.go

@@ -0,0 +1,20 @@
+package router
+
+import "gopkg.in/go-playground/validator.v9"
+
+// NewValidator func
+func NewValidator() *Validator {
+	return &Validator{
+		validator: validator.New(),
+	}
+}
+
+// Validator struct
+type Validator struct {
+	validator *validator.Validate
+}
+
+// Validate func
+func (v *Validator) Validate(i interface{}) error {
+	return v.validator.Struct(i)
+}