feat: add referral network graph visualization page

Interactive Sigma.js + graphology graph with ForceAtlas2 web worker
layout, campaign/user node coloring, filters via nodeReducer pattern,
search highlighting, user/campaign detail side panels, and 4-locale
translations. Dependencies: sigma v3, graphology, graphology-layout-forceatlas2.

package.json

@@ -41,6 +41,9 @@
     "cmdk": "^1.1.1",
     "dompurify": "^3.3.1",
     "framer-motion": "^12.29.2",
+    "graphology": "^0.26.0",
+    "graphology-layout-forceatlas2": "^0.10.1",
+    "graphology-types": "^0.24.8",
     "i18next": "^25.8.4",
     "i18next-browser-languagedetector": "^8.2.0",
     "jsencrypt": "^3.5.4",
@@ -51,6 +54,7 @@
     "react-router": "^7.13.0",
     "react-twemoji": "^0.7.2",
     "recharts": "^3.7.0",
+    "sigma": "^3.0.2",
     "simplex-noise": "^4.0.3",
     "tailwind-merge": "^3.4.0",
     "zustand": "^5.0.11"