fix(aia,ssa,asl,infra): harden SSE transport and stabilize attachment context

Deliver SSE protocol hardening for SAE/HTTP2 paths, add graceful shutdown health behavior, and improve SSA retry UX for transient stream failures. For AIA, persist attachment extraction results in database with cache read-through fallback, plus production cache safety guard to prevent memory-cache drift in multi-instance deployments; also restore ASL SR page scrolling behavior.

Made-with: Cursor

backend/src/modules/asl/extraction/controllers/ExtractionController.ts

@@ -202,7 +202,6 @@ export async function streamTaskLogs(
   reply.raw.writeHead(200, {
     'Content-Type': 'text/event-stream',
     'Cache-Control': 'no-cache',
-    Connection: 'keep-alive',
     'X-Accel-Buffering': 'no',
   });