✨ feat: Implement Resumable Generation Jobs with SSE Support

- Introduced GenerationJobManager to handle resumable LLM generation jobs independently of HTTP connections.
- Added support for subscribing to ongoing generation jobs via SSE, allowing clients to reconnect and receive updates without losing progress.
- Enhanced existing agent controllers and routes to integrate resumable functionality, including job creation, completion, and error handling.
- Updated client-side hooks to manage adaptive SSE streams, switching between standard and resumable modes based on user settings.
- Added UI components and settings for enabling/disabling resumable streams, improving user experience during unstable connections.

api/server/middleware/setHeaders.js

@@ -1,4 +1,9 @@
 function setHeaders(req, res, next) {
+  // Skip SSE headers for resumable mode - it returns JSON first, then client subscribes separately
+  if (req.query.resumable === 'true') {
+    return next();
+  }
+
   res.writeHead(200, {
     Connection: 'keep-alive',
     'Content-Type': 'text/event-stream',