fix(headroom): support Docker sidecar proxy

Treat configured Headroom proxy as running when its /health endpoint
responds, even if local headroom CLI is not installed. Dashboard
Start/Stop stays limited to local loopback proxies while external
Docker sidecars can be enabled via HEADROOM_URL.

Closes #1948

Co-authored-by: Cursor <cursoragent@cursor.com>

src/sse/handlers/chat.js

@@ -11,6 +11,7 @@ import { cacheClaudeHeaders } from "open-sse/utils/claudeHeaderCache.js";
 import { getSettings } from "@/lib/localDb";
 import { getModelInfo, getComboModels } from "../services/model.js";
 import { handleChatCore } from "open-sse/handlers/chatCore.js";
+import { DEFAULT_HEADROOM_URL } from "@/lib/headroom/detect";
 import { errorResponse, unavailableResponse } from "open-sse/utils/error.js";
 import { handleComboChat, handleFusionChat } from "open-sse/services/combo.js";
 import { handleBypassRequest } from "open-sse/utils/bypassHandler.js";
@@ -252,7 +253,7 @@ async function handleSingleModelChat(body, modelStr, clientRawRequest = null, re
       ccFilterNaming: !!chatSettings.ccFilterNaming,
       rtkEnabled: !!chatSettings.rtkEnabled,
       headroomEnabled: !!chatSettings.headroomEnabled,
-      headroomUrl: chatSettings.headroomUrl || "http://localhost:8787",
+      headroomUrl: chatSettings.headroomUrl || DEFAULT_HEADROOM_URL,
       headroomCompressUserMessages: !!chatSettings.headroomCompressUserMessages,
       cavemanEnabled: !!chatSettings.cavemanEnabled,
       cavemanLevel: chatSettings.cavemanLevel || "full",