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>

frontend/public/openapi.json

@@ -2878,6 +2878,13 @@
           "publicKey": {
             "type": "string"
           },
+          "routeOutboundTag": {
+            "type": "string"
+          },
+          "routeThroughXray": {
+            "description": "RouteThroughXray, when true, is the inbound-wide default: every peer\nTPROXYs into Xray unless it explicitly turns its own RouteThroughXray\noff... except a plain bool can't distinguish \"peer left it unset\" from\n\"peer explicitly opted out\", so in practice this ORs with each peer's\nown flag (see Peer.RouteThroughXray) — turning this on routes every\npeer, turning it off still lets individual peers opt in on their own.\nRouteOutboundTag is the default outbound/balancer tag used when a\nrouted peer didn't set its own; empty means Xray's default routing.",
+            "type": "boolean"
+          },
           "s1": {
             "type": "integer"
           },