feat: découverte automatique des nœuds squid via duniter_peerings

- PeerDiscovery.ts : appel duniter_peerings sur rpc.duniter.org, extraction
  des endpoints squid, normalisation URLs, cache localStorage 24h
- EndpointPopover : section "Réseau Ğ1" avec nœuds découverts auto-testés
  à l'ouverture, bouton actualiser pour forcer un refresh du cache
- FlowMap : zone de hit des arcs réduite (max 12→4 px) pour ne plus
  interférer avec le zoom/déplacement de la carte

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

src/services/PeerDiscovery.ts

@@ -0,0 +1,62 @@
+const DUNITER_RPC = 'https://rpc.duniter.org';
+const CACHE_KEY = 'geoflux-peers-v1';
+const CACHE_TTL_MS = 24 * 60 * 60 * 1000;
+
+interface PeerCache {
+  urls: string[];
+  fetchedAt: number;
+}
+
+function normalizeSquidUrl(raw: string): string {
+  const url = raw.replace(/\/$/, '');
+  return url.endsWith('/v1/graphql') ? url : `${url}/v1/graphql`;
+}
+
+export async function discoverSquidNodes(): Promise<string[]> {
+  try {
+    const cached = localStorage.getItem(CACHE_KEY);
+    if (cached) {
+      const parsed: PeerCache = JSON.parse(cached);
+      if (Date.now() - parsed.fetchedAt < CACHE_TTL_MS) return parsed.urls;
+    }
+  } catch { /* ignore */ }
+
+  const controller = new AbortController();
+  const timer = setTimeout(() => controller.abort(), 8_000);
+  try {
+    const res = await fetch(DUNITER_RPC, {
+      method: 'POST',
+      headers: { 'Content-Type': 'application/json' },
+      body: JSON.stringify({ jsonrpc: '2.0', method: 'duniter_peerings', params: [], id: 1 }),
+      signal: controller.signal,
+    });
+    const data = await res.json();
+    const peers: { peer_id: string; endpoints: { protocol: string; address: string }[] }[] =
+      data?.result?.peerings ?? [];
+
+    const seen = new Set<string>();
+    const urls: string[] = [];
+    for (const peer of peers) {
+      for (const ep of peer.endpoints ?? []) {
+        if (ep.protocol === 'squid' && ep.address) {
+          const normalized = normalizeSquidUrl(ep.address);
+          if (!seen.has(normalized)) {
+            seen.add(normalized);
+            urls.push(normalized);
+          }
+        }
+      }
+    }
+
+    localStorage.setItem(CACHE_KEY, JSON.stringify({ urls, fetchedAt: Date.now() }));
+    return urls;
+  } catch {
+    return [];
+  } finally {
+    clearTimeout(timer);
+  }
+}
+
+export function clearPeerCache(): void {
+  localStorage.removeItem(CACHE_KEY);
+}