fix(amneziawg): make RouteViaXray an inbound-level option too

RouteThroughXray/RouteOutboundTag were client-only, but the more common
case is "route this whole AmneziaWG server's traffic through Xray", not
configuring every peer individually. Add the same pair to ServerSettings
(inbound-level) while keeping the per-client fields as an override —
matching how ExternalInterface/IPv6Enabled already work at the server
level next to per-client settings like ForwardedPorts.

Effective per-peer decision (computed once, in InstanceFromInbound, not
duplicated at each consumer):
  - routed = client.RouteThroughXray || server.RouteThroughXray
  - outbound tag = client's own if set, else the server's default

This means a peer can be routed by the inbound-wide default with no
config of its own, opt in on its own even when the default is off, or
keep the default's on/off but pick a different outbound than everyone
else.

internal/web/service/xray.go's injectAmneziawgEgress now calls
amneziawg.InstanceFromInbound instead of re-parsing InboundSettings and
reading model.Client fields directly — the same effective-routing
computation the kernel-side TPROXY rules use, so the two independent
reconcile loops (Xray-config generation and the AWG manager) can never
quietly disagree about which peers are actually routed.

Frontend: Switch + conditional outbound Select added to the AWG inbound
form (mirroring the client-form version and mtproto's own UI), plus the
inbound-defaults.ts default-object fix that's bitten this project's CI
before (Phase 2a) whenever ServerSettings gains a new required-shaped
field.

Test fixtures in xray_config_inject_test.go needed a real Server block
and PublicKey once injectAmneziawgEgress started requiring a usable
InstanceFromInbound result — both were implicit fixture gaps, not
behavior the old tests were actually asserting.

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

internal/web/translation/ru-RU.json

@@ -1828,6 +1828,11 @@
         "ipv6SubnetHint": "Например, fd86:ea04:1115::/64. Обязательно при включённом IPv6.",
         "ipv6ExternalInterface": "Внешний интерфейс для IPv6",
         "ipv6ExternalInterfaceHint": "Сетевой интерфейс хоста для записей NDP-прокси. Оставьте пустым, чтобы использовать «Внешний интерфейс».",
+        "routeThroughXray": "Маршрутизировать через Xray (все клиенты)",
+        "routeThroughXrayHint": "Направлять трафик всех клиентов через Xray по умолчанию вместо прямого выхода через сетевой интерфейс сервера. Клиент может включить это индивидуально, даже если здесь выключено.",
+        "routeOutboundTag": "Исходящий по умолчанию",
+        "routeOutboundTagHint": "Исходящий (outbound) или балансировщик Xray по умолчанию для клиентов, маршрутизируемых через Xray. Собственный выбор клиента имеет приоритет. Оставьте пустым для маршрутизации Xray по умолчанию.",
+        "routeOutboundTagPlaceholder": "Выберите исходящий",
         "obfuscation": "Параметры обфускации",
         "regenerateObfuscation": "Сгенерировать заново",
         "jc": "Jc (кол-во мусорных пакетов)",