feat(headroom): add proxy lifecycle management + dashboard UI

Build on the optional Headroom Token Saver from Carmelo Campos
(PR: feat: add optional Headroom token saver). Add managed start/stop
of the local headroom proxy from the dashboard, install detection,
status probing, and a simplified Token Saver UI.

- detect headroom CLI + python>=3.10, probe proxy /health
- spawn/stop proxy as a detached, pid-tracked process
- /api/headroom/{status,start,stop} routes, gated local-only in dashboardGuard
- one-click Start/Stop Headroom modal, no manual config needed
- claude<->openai shape conversion for /v1/compress via 9router translators

Thanks to Carmelo Campos (@carmelogunsroses) for the original Headroom integration.

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

open-sse/executors/default.js

@@ -116,6 +116,11 @@ export class DefaultExecutor extends BaseExecutor {
   }
 
   buildUrl(model, stream, urlIndex = 0, credentials = null) {
+    // Runtime transport (multi-endpoint providers): use the sourceFormat-matched endpoint
+    const rt = credentials?.runtimeTransport;
+    if (rt?.baseUrl) {
+      return rt.urlSuffix ? `${rt.baseUrl}${rt.urlSuffix}` : rt.baseUrl;
+    }
     if (this.provider?.startsWith?.("openai-compatible-")) {
       const baseUrl = credentials?.providerSpecificData?.baseUrl || OPENAI_COMPAT_BASE;
       const normalized = baseUrl.replace(/\/$/, "");
@@ -156,8 +161,9 @@ export class DefaultExecutor extends BaseExecutor {
   }
 
   buildHeaders(credentials, stream = true) {
-    const headers = { "Content-Type": "application/json", ...this.config.headers };
-    const desc = AUTH_DESCRIPTORS[this.provider] || this.resolveAuthDescriptor();
+    const rt = credentials?.runtimeTransport;
+    const headers = { "Content-Type": "application/json", ...(rt ? rt.headers : this.config.headers) };
+    const desc = rt?.auth || AUTH_DESCRIPTORS[this.provider] || this.resolveAuthDescriptor();
     // Hooks run BEFORE auth so dynamic overlays (claude cached headers) can't clobber the token.
     for (const hook of desc.hooks || []) HEADER_HOOKS[hook]?.(headers, credentials);
     applyAuth(headers, desc, credentials);