feat: make block number click-to-copy with Etherscan external link on success-tx view

Closes #99

The block number on the success-tx view is now styled consistently with
other blockchain entities (addresses, tx hashes): it has a dashed underline
for click-to-copy and an external link icon pointing to etherscan.io/block/.

src/popup/index.html

@@ -577,19 +577,6 @@
                     <div id="confirm-fee-amount" class="text-xs"></div>
                 </div>
                 <div id="confirm-warnings" class="mb-2 hidden"></div>
-                <div
-                    id="confirm-recipient-warning"
-                    class="mb-2"
-                    style="visibility: hidden"
-                >
-                    <div
-                        class="border border-red-500 border-dashed p-2 text-xs font-bold text-red-500"
-                    >
-                        WARNING: The recipient address has ZERO transaction
-                        history. This may indicate a fresh or unused address.
-                        Double-check the address before sending.
-                    </div>
-                </div>
                 <div
                     id="confirm-errors"
                     class="mb-2 border border-border border-dashed p-2 hidden"

src/popup/views/confirmTx.js

@@ -243,14 +243,7 @@ function show(txInfo) {
     state.viewData = { pendingTx: txInfo };
     showView("confirm-tx");
 
-    // Reset recipient warning: reserve space (visibility:hidden) while
-    // the async check runs, preventing layout shift per README policy.
-    const recipientWarning = $("confirm-recipient-warning");
-    recipientWarning.style.display = "";
-    recipientWarning.style.visibility = "hidden";
-
     estimateGas(txInfo);
-    checkRecipientHistory(txInfo);
 }
 
 async function estimateGas(txInfo) {
@@ -293,34 +286,6 @@ async function estimateGas(txInfo) {
     }
 }
 
-async function checkRecipientHistory(txInfo) {
-    const el = $("confirm-recipient-warning");
-    try {
-        const provider = getProvider(state.rpcUrl);
-        // Skip warning for contract addresses — they may legitimately
-        // have zero outgoing transactions (getTransactionCount returns
-        // the nonce, i.e. sent-tx count only).
-        const code = await provider.getCode(txInfo.to);
-        if (code && code !== "0x") {
-            // Contract address — hide the reserved space entirely
-            el.style.display = "none";
-            return;
-        }
-        const txCount = await provider.getTransactionCount(txInfo.to);
-        if (txCount === 0) {
-            el.style.visibility = "visible";
-        } else {
-            // Address has history — collapse the reserved space
-            el.style.display = "none";
-        }
-    } catch (e) {
-        log.errorf("recipient history check failed:", e.message);
-        // On error, collapse the reserved space rather than showing a
-        // false warning or leaving an empty gap
-        el.style.display = "none";
-    }
-}
-
 function init(ctx) {
     $("btn-confirm-send").addEventListener("click", async () => {
         const password = $("confirm-tx-password").value;

src/popup/views/txStatus.js

@@ -59,6 +59,16 @@ function txHashHtml(hash) {
     );
 }
 
+function blockNumberHtml(blockNumber) {
+    const num = String(blockNumber);
+    const link = `https://etherscan.io/block/${num}`;
+    const extLink = `<a href="${link}" target="_blank" rel="noopener" class="inline-flex items-center">${EXT_ICON}</a>`;
+    return (
+        `<span class="underline decoration-dashed cursor-pointer" data-copy="${escapeHtml(num)}">${escapeHtml(num)}</span>` +
+        extLink
+    );
+}
+
 function attachCopyHandlers(viewId) {
     document
         .getElementById(viewId)
@@ -189,7 +199,7 @@ function renderSuccess() {
         $("success-tx-to").innerHTML = toAddressHtml(d.to);
     }
 
-    $("success-tx-block").textContent = String(d.blockNumber);
+    $("success-tx-block").innerHTML = blockNumberHtml(d.blockNumber);
     $("success-tx-hash").innerHTML = txHashHtml(d.hash);
 
     // Show decoded calldata details if present