feat: add fill+border dual-color nodes, radial layout, and dark labels

Node fill color now encodes subscription status (paid/trial active/expired),
while border color indicates referral role (partner/top/active referrer).
Added BFS-based radial initial positioning to spread referral branches outward.
Updated legend with two sections and adjusted FA2 gravity for less clustering.

src/locales/fa.json

@@ -1085,6 +1085,8 @@
       },
       "legend": {
         "title": "راهنما",
+        "fillTitle": "اشتراک",
+        "borderTitle": "نقش ارجاع‌دهنده",
         "regularUser": "کاربر عادی",
         "activeReferrer": "ارجاع‌دهنده فعال",
         "partner": "شریک",