feat: real-time gate messages via SSE + faster push/pull intervals

- Add Server-Sent Events endpoint at GET /api/mesh/gate/stream that
  broadcasts ALL gate events to connected frontends (privacy: no
  per-gate subscriptions, clients filter locally)
- Hook SSE broadcast into all gate event entry points: local append,
  peer push receiver, and pull loop
- Reduce push/pull intervals from 30s to 10s for faster relay sync
- Add useGateSSE hook for frontend EventSource integration
- GateView + MeshChat use SSE for instant refresh, polling demoted
  to 30s fallback

Latency: same-node instant, cross-node ~10s avg (was ~34s)

frontend/src/components/InfonetTerminal/GateView.tsx

@@ -13,6 +13,7 @@ import {
 } from '@/mesh/wormholeIdentityClient';
 import { gateEnvelopeDisplayText, gateEnvelopeState, isEncryptedGateEnvelope } from '@/mesh/gateEnvelope';
 import { validateEventPayload } from '@/mesh/meshSchema';
+import { useGateSSE } from '@/hooks/useGateSSE';
 
 const GATE_INTROS: Record<string, string> = {
   infonet:
@@ -357,11 +358,21 @@ export default function GateView({
     }
   }, [gateId, hydrateMessages]);
 
+  // SSE: instant delivery when new gate events arrive
+  const handleSSEEvent = useCallback(
+    (eventGateId: string) => {
+      if (eventGateId === gateId) void refreshGate();
+    },
+    [gateId, refreshGate],
+  );
+  useGateSSE(handleSSEEvent);
+
+  // Fallback poll (30s) in case SSE disconnects
   useEffect(() => {
     void refreshGate();
     const timer = window.setInterval(() => {
       void refreshGate();
-    }, 8000);
+    }, 30_000);
     return () => {
       window.clearInterval(timer);
     };