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.

src/store/referralNetwork.ts

@@ -0,0 +1,70 @@
+import { create } from 'zustand';
+import type {
+  NetworkGraphData,
+  SelectedNode,
+  NetworkFilters,
+  NetworkUserNode,
+  NetworkCampaignNode,
+} from '@/types/referralNetwork';
+
+const DEFAULT_FILTERS: NetworkFilters = {
+  campaigns: [],
+  partnersOnly: false,
+  minReferrals: 0,
+};
+
+interface ReferralNetworkState {
+  networkData: NetworkGraphData | null;
+  selectedNode: SelectedNode;
+  hoveredNodeId: string | null;
+  highlightedNodes: Set<string>;
+  searchQuery: string;
+  searchResults: { users: NetworkUserNode[]; campaigns: NetworkCampaignNode[] };
+  filters: NetworkFilters;
+  isFiltersOpen: boolean;
+
+  setNetworkData: (data: NetworkGraphData) => void;
+  setSelectedNode: (node: SelectedNode) => void;
+  setHoveredNode: (id: string | null) => void;
+  setHighlightedNodes: (nodes: Set<string>) => void;
+  setSearchQuery: (query: string) => void;
+  setSearchResults: (results: {
+    users: NetworkUserNode[];
+    campaigns: NetworkCampaignNode[];
+  }) => void;
+  updateFilters: (filters: Partial<NetworkFilters>) => void;
+  resetFilters: () => void;
+  setIsFiltersOpen: (open: boolean) => void;
+}
+
+export const useReferralNetworkStore = create<ReferralNetworkState>()((set) => ({
+  networkData: null,
+  selectedNode: null,
+  hoveredNodeId: null,
+  highlightedNodes: new Set<string>(),
+  searchQuery: '',
+  searchResults: { users: [], campaigns: [] },
+  filters: { ...DEFAULT_FILTERS },
+  isFiltersOpen: false,
+
+  setNetworkData: (data) => set({ networkData: data }),
+
+  setSelectedNode: (node) => set({ selectedNode: node }),
+
+  setHoveredNode: (id) => set({ hoveredNodeId: id }),
+
+  setHighlightedNodes: (nodes) => set({ highlightedNodes: nodes }),
+
+  setSearchQuery: (query) => set({ searchQuery: query }),
+
+  setSearchResults: (results) => set({ searchResults: results }),
+
+  updateFilters: (partial) =>
+    set((state) => ({
+      filters: { ...state.filters, ...partial },
+    })),
+
+  resetFilters: () => set({ filters: { ...DEFAULT_FILTERS } }),
+
+  setIsFiltersOpen: (open) => set({ isFiltersOpen: open }),
+}));