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/lib/db/repos/settingsRepo.js

@@ -2,6 +2,7 @@ import { getAdapter } from "../driver.js";
 import { parseJson, stringifyJson } from "../helpers/jsonCol.js";
 
 const DEFAULT_MITM_ROUTER_BASE = "http://localhost:20128";
+const DEFAULT_HEADROOM_URL = process.env.HEADROOM_URL || "http://localhost:8787";
 
 const DEFAULT_SETTINGS = {
   cloudEnabled: false,
@@ -35,7 +36,7 @@ const DEFAULT_SETTINGS = {
   dnsToolEnabled: {},
   rtkEnabled: true,
   headroomEnabled: false,
-  headroomUrl: "http://localhost:8787",
+  headroomUrl: DEFAULT_HEADROOM_URL,
   headroomCompressUserMessages: false,
   cavemanEnabled: false,
   cavemanLevel: "full",