[management] detach JWT group sync write from request cancellation (#6621)

The HTTP auth middleware runs syncUserJWTGroups in the request context.
The dashboard SPA routinely aborts in-flight requests on re-render or
navigation, which cancels the request context mid-write and rolls back
the group-sync DB transaction. The error is logged but swallowed, so the
synced groups silently never persist (users.auto_groups stays empty)
while the failing log line repeats on every request.

Detach the sync from the request's cancellation with
context.WithoutCancel so the write can commit regardless of the client
connection; the store already bounds the transaction with its own
timeout. Add a regression test asserting the sync receives a
non-cancelled context even when the originating request is cancelled.

management/server/http/middleware/auth_middleware.go

@@ -152,7 +152,11 @@ func (m *AuthMiddleware) checkJWTFromRequest(r *http.Request, authHeaderParts []
 		return err
 	}
 
-	err = m.syncUserJWTGroups(ctx, userAuth)
+	// Detach the group-sync write from the request's cancellation: the dashboard
+	// SPA aborts in-flight requests on re-render, which would otherwise cancel the
+	// DB transaction mid-write and silently drop the synced groups. Context values
+	// (request id, logger) are preserved; the store bounds the tx with its own timeout.
+	err = m.syncUserJWTGroups(context.WithoutCancel(ctx), userAuth)
 	if err != nil {
 		log.WithContext(ctx).Errorf("HTTP server failed to sync user JWT groups: %s", err)
 	}