refactor(witness,refinery): ZFC-compliant state management

Remove state files from witness and refinery managers, following
the "Discover, Don't Track" principle. Tmux session existence is
now the source of truth for running state (like deacon).

Changes:
- Add IsRunning() that checks tmux HasSession
- Change Status() to return *tmux.SessionInfo
- Remove loadState/saveState/stateManager
- Simplify Start()/Stop() to not use state files
- Update CLI commands (witness/refinery/rig) for new API
- Update tests to be ZFC-compliant

This fixes state file divergence issues where witness/refinery
could show "running" when the actual tmux session was dead.

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

internal/cmd/refinery.go

@@ -337,6 +337,14 @@ func runRefineryStop(cmd *cobra.Command, args []string) error {
 	return nil
 }
 
+// RefineryStatusOutput is the JSON output format for refinery status.
+type RefineryStatusOutput struct {
+	Running     bool   `json:"running"`
+	RigName     string `json:"rig_name"`
+	Session     string `json:"session,omitempty"`
+	QueueLength int    `json:"queue_length"`
+}
+
 func runRefineryStatus(cmd *cobra.Command, args []string) error {
 	rigName := ""
 	if len(args) > 0 {
@@ -348,58 +356,42 @@ func runRefineryStatus(cmd *cobra.Command, args []string) error {
 		return err
 	}
 
-	ref, err := mgr.Status()
-	if err != nil {
-		return fmt.Errorf("getting status: %w", err)
-	}
+	// ZFC: tmux is source of truth for running state
+	running, _ := mgr.IsRunning()
+	sessionInfo, _ := mgr.Status() // may be nil if not running
+
+	// Get queue from beads
+	queue, _ := mgr.Queue()
+	queueLen := len(queue)
 
 	// JSON output
 	if refineryStatusJSON {
+		output := RefineryStatusOutput{
+			Running:     running,
+			RigName:     rigName,
+			QueueLength: queueLen,
+		}
+		if sessionInfo != nil {
+			output.Session = sessionInfo.Name
+		}
 		enc := json.NewEncoder(os.Stdout)
 		enc.SetIndent("", "  ")
-		return enc.Encode(ref)
+		return enc.Encode(output)
 	}
 
 	// Human-readable output
 	fmt.Printf("%s Refinery: %s\n\n", style.Bold.Render("⚙"), rigName)
 
-	stateStr := string(ref.State)
-	switch ref.State {
-	case refinery.StateRunning:
-		stateStr = style.Bold.Render("● running")
-	case refinery.StateStopped:
-		stateStr = style.Dim.Render("○ stopped")
-	case refinery.StatePaused:
-		stateStr = style.Dim.Render("⏸ paused")
-	}
-	fmt.Printf("  State: %s\n", stateStr)
-
-	if ref.StartedAt != nil {
-		fmt.Printf("  Started: %s\n", ref.StartedAt.Format("2006-01-02 15:04:05"))
-	}
-
-	if ref.CurrentMR != nil {
-		fmt.Printf("\n  %s\n", style.Bold.Render("Currently Processing:"))
-		fmt.Printf("    Branch: %s\n", ref.CurrentMR.Branch)
-		fmt.Printf("    Worker: %s\n", ref.CurrentMR.Worker)
-		if ref.CurrentMR.IssueID != "" {
-			fmt.Printf("    Issue:  %s\n", ref.CurrentMR.IssueID)
+	if running {
+		fmt.Printf("  State: %s\n", style.Bold.Render("● running"))
+		if sessionInfo != nil {
+			fmt.Printf("  Session: %s\n", sessionInfo.Name)
 		}
+	} else {
+		fmt.Printf("  State: %s\n", style.Dim.Render("○ stopped"))
 	}
 
-	// Get queue length
-	queue, _ := mgr.Queue()
-	pendingCount := 0
-	for _, item := range queue {
-		if item.Position > 0 { // Not currently processing
-			pendingCount++
-		}
-	}
-	fmt.Printf("\n  Queue: %d pending\n", pendingCount)
-
-	if ref.LastMergeAt != nil {
-		fmt.Printf("  Last merge: %s\n", ref.LastMergeAt.Format("2006-01-02 15:04:05"))
-	}
+	fmt.Printf("\n  Queue: %d pending\n", queueLen)
 
 	return nil
 }