feat(nodes): add renewal cycle and auto-advance scheduling (#296)

- Add renewal_cycle field to nodes for tracking paid vs free cycles
- Implement auto-advance scheduling when renewal is processed
- Add migration test for renewal_cycle column
- Update dashboard to show renewal cycle count
- Add renewal status display on node detail page

go-backend/internal/http/handler/jobs_renewal_test.go

@@ -0,0 +1,55 @@
+package handler
+
+import (
+	"database/sql"
+	"testing"
+	"time"
+
+	"go-backend/internal/store/repo"
+)
+
+func TestRunNodeRenewalCycleJob_AdvancesOverdueAnchorTimes(t *testing.T) {
+	dbPath := t.TempDir() + "/renewal-test.db"
+	r, err := repo.Open(dbPath)
+	if err != nil {
+		t.Fatalf("open repo: %v", err)
+	}
+	t.Cleanup(func() {
+		_ = r.Close()
+	})
+
+	now := time.Date(2026, 3, 8, 12, 0, 0, 0, time.UTC)
+	nowMs := now.UnixMilli()
+
+	nodeID := int64(101)
+	err = r.DB().Exec(`
+		INSERT INTO node (id, name, secret, server_ip, port, http, tls, socks, created_time, status, renewal_cycle, expiry_time)
+		VALUES (?, ?, ?, ?, ?, ?, ?, ?, ?, ?, ?, ?)
+	`, nodeID, "no-cycle-node", "test-secret", "192.168.1.1", "1000-65535", 1, 1, 1, nowMs, 1, "", nil).Error
+	if err != nil {
+		t.Fatalf("insert test node: %v", err)
+	}
+
+	quarterNodeID := int64(102)
+	err = r.DB().Exec(`
+		INSERT INTO node (id, name, secret, server_ip, port, http, tls, socks, created_time, status, renewal_cycle, expiry_time)
+		VALUES (?, ?, ?, ?, ?, ?, ?, ?, ?, ?, ?, ?)
+	`, quarterNodeID, "quarter-node", "test-secret", "192.168.1.1", "1000-65535", 1, 1, 1, nowMs, 1, "quarter", now.AddDate(0, -4, 0).UnixMilli()).Error
+	if err != nil {
+		t.Fatalf("insert test node: %v", err)
+	}
+
+	h := &Handler{repo: r}
+	h.runNodeRenewalCycleJob(now)
+
+	var anchor sql.NullInt64
+	err = r.DB().Raw(`SELECT expiry_time FROM node WHERE id = ?`, quarterNodeID).Row().Scan(&anchor)
+	if err != nil {
+		t.Fatalf("query expiry_time: %v", err)
+	}
+
+	expectedAnchor := now.AddDate(0, 2, 0).UnixMilli()
+	if !anchor.Valid || anchor.Int64 != expectedAnchor {
+		t.Fatalf("expected anchor %d (2026-05-08), got %d", expectedAnchor, anchor.Int64)
+	}
+}