feat(P05): drain + daemon drain-and-stop (REQ-061) + job migrate (REQ-116)

orca node drain <host>: marks draining, stops allocs via SSH, marks
drained. orca daemon drain-and-stop: stops v0.8 daemons on peers.
orca job migrate <name> --to <node>: drain+reschedule composite
(C3=a, not live-migrate). Node states: draining, drained.

---ci---
project: orca
phase: 05
milestone: v0.11
status: execute
---/ci---

internal/store/node_repo.go

@@ -154,6 +154,24 @@ func (r *NodeRepo) Delete(ctx context.Context, id string) error {
 	return nil
 }
 
+// SetNodeState updates a node's state to the given string value
+// (REQ-061). Unlike UpdateState, which takes a model.NodeState, this
+// accepts a raw string so callers can set arbitrary states (draining,
+// drained) without coupling to every constant in the model package.
+func (r *NodeRepo) SetNodeState(ctx context.Context, nodeID, state string) error {
+	res, err := r.db.ExecContext(ctx,
+		`UPDATE nodes SET state = ?, last_seen = ? WHERE id = ?`,
+		state, time.Now().UTC(), nodeID)
+	if err != nil {
+		return fmt.Errorf("update node state: %w", err)
+	}
+	rows, _ := res.RowsAffected()
+	if rows == 0 {
+		return ErrNotFound
+	}
+	return nil
+}
+
 type scanner interface {
 	Scan(dest ...any) error
 }