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>

src/app/(dashboard)/dashboard/endpoint/endpointConstants.js

@@ -24,3 +24,9 @@ export const CAVEMAN_LEVELS = [
   { id: "wenyan", label: "文 Full", desc: "Maximum 文言文, 80-90% reduction", wenyan: true },
   { id: "wenyan-ultra", label: "文 Ultra", desc: "Extreme classical compression", wenyan: true },
 ];
+
+export const PONYTAIL_LEVELS = [
+  { id: "lite", label: "Lite", desc: "Build asked, name lazier option" },
+  { id: "full", label: "Full", desc: "Ladder enforced: stdlib/native first" },
+  { id: "ultra", label: "Ultra", desc: "YAGNI extremist, deletion first" },
+];