Fix duplicate entries in viewer caused by untracked SDK agent promise (#86)

* Initial plan

* Initial analysis: Found root cause of double entries bug

Co-authored-by: thedotmack <683968+thedotmack@users.noreply.github.com>

* Fix double entries by assigning generatorPromise in handleSessionInit

Co-authored-by: thedotmack <683968+thedotmack@users.noreply.github.com>

---------

Co-authored-by: copilot-swe-agent[bot] <198982749+Copilot@users.noreply.github.com>
Co-authored-by: thedotmack <683968+thedotmack@users.noreply.github.com>
Co-authored-by: Alex Newman <thedotmack@gmail.com>

src/services/worker-service.ts

@@ -262,7 +262,7 @@ export class WorkerService {
       this.broadcastProcessingStatus(true);
 
       // Start SDK agent in background (pass worker ref for spinner control)
-      this.sdkAgent.startSession(session, this).catch(err => {
+      session.generatorPromise = this.sdkAgent.startSession(session, this).catch(err => {
         logger.failure('WORKER', 'SDK agent error', { sessionId: sessionDbId }, err);
       });