fix: streaming timeout + WebSocket close guard

- Streaming httpx client uses 300s read timeout (cloud LLMs can take
  30-60s for first token). Was using 120s general timeout.
- Guard all WebSocket sends with try/except for client disconnect.
  Prevents "Cannot send once close message has been sent" crash.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

packages/gateway/gateway/channels/web.py

@@ -362,21 +362,25 @@ async def _handle_websocket_connection(
                 current_tenant_id.reset(rls_token2)
 
             # Signal stream completion to the client
-            await websocket.send_json({
-                "type": "done",
-                "text": response_text,
-                "conversation_id": saved_conversation_id,
-            })
+            try:
+                await websocket.send_json({
+                    "type": "done",
+                    "text": response_text,
+                    "conversation_id": saved_conversation_id,
+                })
+            except Exception:
+                pass  # Client already disconnected
         else:
             logger.warning(
-                "No response received within %ds for conversation=%s",
-                _RESPONSE_TIMEOUT_SECONDS,
-                saved_conversation_id,
+                "No response received for conversation=%s", saved_conversation_id,
             )
-            await websocket.send_json({
-                "type": "error",
-                "message": "Agent did not respond in time. Please try again.",
-            })
+            try:
+                await websocket.send_json({
+                    "type": "error",
+                    "message": "I'm having trouble responding right now. Please try again.",
+                })
+            except Exception:
+                pass  # Client already disconnected
 
 
 @web_chat_router.websocket("/chat/ws/{conversation_id}")