feat(wireguard): multi-client support

WireGuard inbounds now manage per-client peers using xray-core's native WireGuard users (AddUser/RemoveUser). Each client lives in settings.clients (canonical, like every other protocol) and is projected to peers[] only when emitting the xray config, at level 0 so the dispatcher's per-user traffic/online counters work with no extra plumbing.

Backend: internal/util/wireguard gains KeyToHex (base64 to hex for the gRPC path), PublicKeyFromPrivate and GenerateWireguardPSK; xray/api.go builds a wireguard account in AddUser with hex keys (RemoveUser already worked); client CRUD generates a keypair and allocates a unique tunnel address per client and never rotates keys on edit; an idempotent migration converts legacy settings.peers into managed clients; WireGuard is included in the raw subscription.

Frontend: WireGuard in the add-client modal with keys on the credential tab, client schema, per-client QR/link/.conf, inbound form reduced to server settings; i18n added across 13 locales.

Fix: guard the settings[clients] assertion in add/update so a legacy WireGuard inbound stored without a clients key no longer panics.

frontend/src/pages/clients/ClientBulkAddModal.tsx

@@ -16,7 +16,7 @@ import { ClientBulkAddFormSchema, type ClientBulkAddFormValues } from '@/schemas
 const FLOW_OPTIONS = Object.values(TLS_FLOW_CONTROL);
 
 const MULTI_CLIENT_PROTOCOLS = new Set([
-  'shadowsocks', 'vless', 'vmess', 'trojan', 'hysteria',
+  'shadowsocks', 'vless', 'vmess', 'trojan', 'hysteria', 'wireguard',
 ]);
 
 interface ClientBulkAddModalProps {