feat: add due date filters for list command

- --due: show only nodes with a due date set
- --due-within N: show only nodes due within N days (includes overdue)

Implemented in service layer with post-fetch filtering, threaded through
API client and server, and exposed via CLI flags.

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

src/service/api_client.go

@@ -8,6 +8,7 @@ import (
 	"fmt"
 	"net/http"
 	"net/url"
+	"strconv"
 )
 
 type apiClient struct {
@@ -78,6 +79,12 @@ func (c *apiClient) List(filter ListFilter) ([]*models.Node, error) {
 			q.Add("rel", string(r.Type)+":"+r.Target)
 		}
 	}
+	if filter.HasDueDate {
+		q.Set("has_due_date", "true")
+	}
+	if filter.DueWithin != nil {
+		q.Set("due_within", strconv.Itoa(*filter.DueWithin))
+	}
 	path := "/nodes"
 	if len(q) > 0 {
 		path += "?" + q.Encode()

src/service/node_service.go

@@ -56,7 +56,9 @@ type UpdateInput struct {
 // Tag filters (Target == "") match by rel_name prefix.
 // Edge filters (Target != "") are resolved to node IDs.
 type ListFilter struct {
-	Rels []RelInput
+	Rels       []RelInput
+	HasDueDate bool // when true, only return nodes that have a due date set
+	DueWithin  *int // when non-nil, only return nodes due within this many days (includes overdue)
 }
 
 // RelInput is a typed, directed rel with a target that may be a name or node ID.

src/service/node_service_impl.go

@@ -234,6 +234,26 @@ func (s *nodeServiceImpl) List(filter ListFilter) ([]*models.Node, error) {
 			result = append(result, n)
 		}
 	}
+
+	if filter.HasDueDate || filter.DueWithin != nil {
+		now := time.Now().UTC().Truncate(24 * time.Hour)
+		filtered := result[:0]
+		for _, n := range result {
+			if n.DueDate == nil {
+				continue
+			}
+			if filter.DueWithin != nil {
+				due := n.DueDate.UTC().Truncate(24 * time.Hour)
+				cutoff := now.AddDate(0, 0, *filter.DueWithin)
+				if due.After(cutoff) {
+					continue
+				}
+			}
+			filtered = append(filtered, n)
+		}
+		result = filtered
+	}
+
 	return result, nil
 }