Report queued tasks the scheduling pass never considers

A task in retry backoff was filtered out before the candidate loop, so it
recorded no rejection at all: queued, apparently assignable, and silent. That is
the exact shape that made F5 take a live session to diagnose. It now reports
"retry backoff until <time>".

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

go.mod

@@ -3,6 +3,7 @@ module orchestra
 go 1.22
 
 require (
+	go.etcd.io/bbolt v1.3.11
 	golang.org/x/crypto v0.29.0
 	golang.org/x/term v0.26.0
 )