Mainnet indexer fix + retire testnet copy

- chain.js: derive the chain tip as the MAX height across the RPC pool and scan
  getLogs against that same synced node. Load-balanced public RPCs (publicnode)
  intermittently answer eth_blockNumber from a replica lagging thousands of
  blocks behind, which stalled the mainnet scan (latest < lastBlock, 0 events)
  and could skip freshly-mined events. This unblocks the live ledger + the
  purchase-confirmation email (both driven by the event scan).
- disclaimer: replace the "rehearsal/testnet" section with a live-on-Polygon
  real-money notice (it's live now).
- Point the dead Amoy fallbacks (purchase email tx link, contract-page source
  link) at Polygon mainnet / the verified mainnet contract.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

chain.js

@@ -189,15 +189,36 @@ function saveState() {
     fs.renameSync(tmp, STATE_FILE);
   } catch (e) { console.error('chain state save failed', e.message); }
 }
+// Most-synced tip across the RPC pool. Public load-balanced nodes (publicnode)
+// sometimes answer eth_blockNumber from a replica lagging thousands of blocks
+// behind — which stalls the scan (latest < lastBlock) and, worse, could let a
+// getLogs from a lagging node skip freshly-mined events for good. Take the MAX
+// height and remember which node reported it, so we scan against a node we know
+// is synced to that height.
+async function bestTip() {
+  const urls = getConfig().rpcs;
+  let best = { block: 0, url: urls[0] };
+  await Promise.all(urls.map(async u => {
+    try { const b = parseInt(await rpcOnce(u, 'eth_blockNumber', []), 16);
+      if (b > best.block) best = { block: b, url: u }; } catch (e) {}
+  }));
+  return best;
+}
 async function tail() {
   if (busy) return; busy = true;
   try {
-    const latest = parseInt(await rpc('eth_blockNumber', []), 16);
+    const tip = await bestTip();
+    const latest = tip.block;
     while (state.lastBlock < latest) {
       const from = state.lastBlock + 1;
       const to = Math.min(from + CHUNK - 1, latest);
-      const logs = await rpc('eth_getLogs', [{ address: getConfig().contract,
-        fromBlock: '0x' + from.toString(16), toBlock: '0x' + to.toString(16) }]);
+      // scan against the node we confirmed is synced to `latest`; fall back to
+      // the rotating pool only if that specific node errors on this range.
+      let logs;
+      try { logs = await rpcOnce(tip.url, 'eth_getLogs', [{ address: getConfig().contract,
+        fromBlock: '0x' + from.toString(16), toBlock: '0x' + to.toString(16) }]); }
+      catch (e) { logs = await rpc('eth_getLogs', [{ address: getConfig().contract,
+        fromBlock: '0x' + from.toString(16), toBlock: '0x' + to.toString(16) }]); }
       for (const lg of logs) {
         const ev = decodeLog(lg);
         if (!ev) continue;