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/test/inbound-defaults.test.ts

@@ -142,10 +142,11 @@ describe('createDefault*InboundSettings factories', () => {
   it('wireguard', () => {
     const s = createDefaultWireguardInboundSettings({
       secretKey: 'QGVlb2dXc1ZTWGw0ZXBzZndsWmtMaUM5MUlNYjBHWFdYbz0=',
-      peerPrivateKey: 'cGVlci1maXh0dXJlLXByaXZhdGUta2V5LWZvci10ZXN0cw==',
     });
     expect(s).toMatchSnapshot();
     expect(WireguardInboundSettingsSchema.parse(s)).toEqual(s);
+    expect(s.peers).toEqual([]);
+    expect(s.clients).toEqual([]);
   });
 });