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/sse/handlers/chat.js

@@ -251,8 +251,13 @@ async function handleSingleModelChat(body, modelStr, clientRawRequest = null, re
       apiKey,
       ccFilterNaming: !!chatSettings.ccFilterNaming,
       rtkEnabled: !!chatSettings.rtkEnabled,
+      headroomEnabled: !!chatSettings.headroomEnabled,
+      headroomUrl: chatSettings.headroomUrl || "http://localhost:8787",
+      headroomCompressUserMessages: !!chatSettings.headroomCompressUserMessages,
       cavemanEnabled: !!chatSettings.cavemanEnabled,
       cavemanLevel: chatSettings.cavemanLevel || "full",
+      ponytailEnabled: !!chatSettings.ponytailEnabled,
+      ponytailLevel: chatSettings.ponytailLevel || "full",
       providerThinking,
       // Detect source format by endpoint + body
       sourceFormatOverride: request?.url ? detectFormatByEndpoint(new URL(request.url).pathname, body) : null,