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>

cli/src/cli/menus/settings.js

@@ -39,6 +39,8 @@ async function showSettingsMenu(breadcrumb = []) {
       // RTK section
       const rtkOn = data?.settings?.rtkEnabled !== false;
       lines.push(`  RTK:      ${rtkOn ? `${COLORS.green}ON${COLORS.reset}` : `${COLORS.red}OFF${COLORS.reset}`} ${COLORS.dim}(Token Saver)${COLORS.reset}`);
+      const headroomOn = data?.settings?.headroomEnabled === true;
+      lines.push(`  Headroom: ${headroomOn ? `${COLORS.green}ON${COLORS.reset}` : `${COLORS.red}OFF${COLORS.reset}`} ${COLORS.dim}(${data?.settings?.headroomUrl || "http://localhost:8787"})${COLORS.reset}`);
 
       // Auth mode section
       const authMode = data?.settings?.authMode || "password";
@@ -73,6 +75,13 @@ async function showSettingsMenu(breadcrumb = []) {
         },
         action: async (d) => { await toggleRtk(d?.settings?.rtkEnabled !== false); return true; }
       },
+      {
+        label: (d) => {
+          const on = d?.settings?.headroomEnabled === true;
+          return `Token Saver (Headroom): ${on ? "ON" : "OFF"} → toggle`;
+        },
+        action: async (d) => { await toggleHeadroom(d?.settings?.headroomEnabled === true); return true; }
+      },
       {
         label: "🔑 Reset Password to Default",
         action: async () => { await resetPassword(); return true; }
@@ -160,6 +169,17 @@ async function toggleRtk(currentlyOn) {
   await pause();
 }
 
+async function toggleHeadroom(currentlyOn) {
+  const next = !currentlyOn;
+  const result = await api.updateSettings({ headroomEnabled: next });
+  if (result.success) {
+    showStatus(`Headroom ${next ? "enabled" : "disabled"}`, "success");
+  } else {
+    showStatus(`Failed: ${result.error}`, "error");
+  }
+  await pause();
+}
+
 /**
  * Reset dashboard password to default via server API (writes the live SQLite DB).
  * After reset, user can log in with the default password "123456".