Add address color dots and cached ENS reverse lookups

Deterministic colored dots derived from address bytes (16-color palette)
displayed before every address. ENS reverse resolution for transaction
counterparties with 12-hour localStorage cache.

src/shared/ens.js

@@ -0,0 +1,57 @@
+// Cached ENS reverse resolution.
+// Resolves addresses to ENS names via ethers provider.lookupAddress(),
+// caching results in localStorage with a 12-hour TTL.
+
+const { getProvider } = require("./balances");
+const { log } = require("./log");
+
+const CACHE_TTL_MS = 43200000; // 12 hours
+const CACHE_PREFIX = "ens:";
+
+function getCached(address) {
+    const key = CACHE_PREFIX + address.toLowerCase();
+    try {
+        const raw = localStorage.getItem(key);
+        if (!raw) return undefined;
+        const entry = JSON.parse(raw);
+        if (Date.now() - entry.ts < CACHE_TTL_MS) {
+            return entry.name;
+        }
+    } catch {
+        // Corrupt cache entry — treat as miss.
+    }
+    return undefined;
+}
+
+function setCache(address, name) {
+    const key = CACHE_PREFIX + address.toLowerCase();
+    localStorage.setItem(key, JSON.stringify({ name, ts: Date.now() }));
+}
+
+async function resolveEnsName(address, rpcUrl) {
+    const cached = getCached(address);
+    if (cached !== undefined) return cached;
+
+    const provider = getProvider(rpcUrl);
+    try {
+        const name = (await provider.lookupAddress(address)) || null;
+        setCache(address, name);
+        return name;
+    } catch (e) {
+        log.errorf("ENS reverse lookup failed", address, e.message);
+        setCache(address, null);
+        return null;
+    }
+}
+
+async function resolveEnsNames(addresses, rpcUrl) {
+    const results = new Map();
+    await Promise.all(
+        addresses.map(async (addr) => {
+            results.set(addr, await resolveEnsName(addr, rpcUrl));
+        }),
+    );
+    return results;
+}
+
+module.exports = { resolveEnsName, resolveEnsNames };