feat(orchestrator): soft occupancy threshold requests handoff early (S11 partial)

Coordinator.Soft (default 0.55, ORCHESTRA_OCCUPANCY_SOFT) makes rotate()
and TurnDecision request a handoff advisory-only once occupancy crosses
the soft threshold, well before Hard forces a release/rotation.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01W1rkJ2hBMybnJctPbcy4tT

cmd/orchestra/main.go

@@ -120,6 +120,9 @@ func main() {
 			if v, parseErr := strconv.ParseFloat(os.Getenv("ORCHESTRA_OCCUPANCY_HARD"), 64); parseErr == nil && v > 0 && v < 1 {
 				hard = v
 			}
+			if v, parseErr := strconv.ParseFloat(os.Getenv("ORCHESTRA_OCCUPANCY_SOFT"), 64); parseErr == nil && v > 0 && v < 1 {
+				coordinator.Soft = v
+			}
 			go func() {
 				if monitorErr := coordinator.Monitor(context.Background(), hard, 30*time.Second); monitorErr != nil {
 					log.Printf("orchestrator monitor: %v", monitorErr)