feat: apply inbound/outbound/routing changes live via Xray gRPC API

Add a hot-apply layer that computes a diff between the old and new
generated config and applies only the changed parts through the Xray
gRPC HandlerService and RoutingService, avoiding a full process restart
whenever possible. A restart is still performed when sections that have
no reload API (log, dns, policy, observatory, ...) actually change.

Key additions:
- internal/xray/hot_diff.go: ComputeHotDiff with canonical-JSON
  comparison (sorted keys, null=absent, full number precision) so UI
  reformatting never triggers a spurious restart
- internal/xray/api.go: AddOutbound/DelOutbound, ApplyRoutingConfig,
  GetBalancerInfo, SetBalancerTarget, TestRoute gRPC wrappers
- internal/web/service/xray.go: tryHotApply, ensureAPIServices,
  GetBalancersStatus, OverrideBalancer, TestRoute service methods
- internal/web/controller/xray_setting.go: balancerStatus,
  balancerOverride, routeTest API endpoints
- frontend: BalancersTab live-status/override columns, RouteTester
  component, Restart button removed (Save now hot-applies)
- balancer-helpers.ts: syncObservatories never creates observatory
  sections for random/roundRobin balancers (no reload API → restart)
- i18n: balancerLive/Override/routeTester keys added to all 13 locales

frontend/src/pages/api-docs/endpoints.ts

@@ -1045,6 +1045,40 @@ export const sections: readonly Section[] = [
         ],
         body: 'outbound={"protocol":"freedom","settings":{}}&mode=tcp',
       },
+      {
+        method: 'POST',
+        path: '/panel/api/xray/balancerStatus',
+        summary: 'Live state of routing balancers in the running core (RoutingService.GetBalancerInfo): current override and the targets the strategy prefers. Returns a map keyed by balancer tag.',
+        params: [
+          { name: 'tags', in: 'body (form)', type: 'string', desc: 'Comma-separated balancer tags to query (e.g. "b1,b2").' },
+        ],
+        body: 'tags=b1,b2',
+      },
+      {
+        method: 'POST',
+        path: '/panel/api/xray/balancerOverride',
+        summary: 'Force a balancer in the running core to always pick one outbound (RoutingService.OverrideBalancerTarget). Applied live without a restart; cleared automatically when Xray restarts.',
+        params: [
+          { name: 'tag', in: 'body (form)', type: 'string', desc: 'Balancer tag (required).' },
+          { name: 'target', in: 'body (form)', type: 'string', desc: 'Outbound tag to force. Empty clears the override and returns control to the strategy.' },
+        ],
+        body: 'tag=b1&target=proxy',
+      },
+      {
+        method: 'POST',
+        path: '/panel/api/xray/routeTest',
+        summary: 'Ask the running core which outbound its router would pick for a synthetic connection (RoutingService.TestRoute). No traffic is sent.',
+        params: [
+          { name: 'domain', in: 'body (form)', type: 'string', desc: 'Target domain. Either domain or ip is required.' },
+          { name: 'ip', in: 'body (form)', type: 'string', desc: 'Target IP. Either domain or ip is required.' },
+          { name: 'port', in: 'body (form)', type: 'number', desc: 'Target port (optional).' },
+          { name: 'network', in: 'body (form)', type: 'string', desc: '"tcp" (default) or "udp".' },
+          { name: 'inboundTag', in: 'body (form)', type: 'string', desc: 'Simulate arrival on this inbound (optional).' },
+          { name: 'protocol', in: 'body (form)', type: 'string', desc: 'Sniffed protocol such as http, tls, bittorrent (optional).' },
+          { name: 'email', in: 'body (form)', type: 'string', desc: 'User attribution for user-based rules (optional).' },
+        ],
+        body: 'domain=example.com&port=443&network=tcp',
+      },
       {
         method: 'GET',
         path: '/panel/api/xray/outbound-subs',