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/lib/db/repos/settingsRepo.js

@@ -34,8 +34,13 @@ const DEFAULT_SETTINGS = {
   mitmRouterBaseUrl: DEFAULT_MITM_ROUTER_BASE,
   dnsToolEnabled: {},
   rtkEnabled: true,
+  headroomEnabled: false,
+  headroomUrl: "http://localhost:8787",
+  headroomCompressUserMessages: false,
   cavemanEnabled: false,
   cavemanLevel: "full",
+  ponytailEnabled: false,
+  ponytailLevel: "full",
 };
 
 async function readRaw() {