feat: add blockie identicon to Identity block in TransactionDetail

Generate a blockie from the transaction hash and display it centered
at the top of the Identity block, matching the pattern used in
AddressDetail and AddressToken views. Updates README to document
the new element.

README.md

@@ -439,6 +439,7 @@ transitions.
   matching the Settings view pattern):
     - "Transaction" heading, "Back" button
     - **Identity block**:
+        - Blockie identicon (48px, centered, derived from transaction hash)
         - Transaction hash: full hash (tap to copy) + etherscan link
         - Type: transaction classification — one of: Native ETH Transfer, ERC-20
           Token Transfer, Swap, Token Approval, Contract Call, Contract Creation

src/popup/index.html

@@ -1068,6 +1068,10 @@
                 <!-- ── Identity ── -->
                 <div class="bg-well p-3 mx-1 mb-3">
                     <h3 class="font-bold mb-1">Identity</h3>
+                    <div
+                        id="tx-detail-blockie"
+                        class="flex justify-center mt-1 mb-3"
+                    ></div>
                     <div class="mb-2">
                         <div class="text-xs text-muted mb-1">
                             Transaction hash

src/popup/views/transactionDetail.js

@@ -130,6 +130,19 @@ function render() {
     if (!tx) return;
     $("tx-detail-hash").innerHTML = txHashHtml(tx.hash);
 
+    // Blockie identicon for the transaction hash
+    const blockieEl = $("tx-detail-blockie");
+    if (blockieEl) {
+        blockieEl.innerHTML = "";
+        const img = document.createElement("img");
+        img.src = makeBlockie(tx.hash);
+        img.width = 48;
+        img.height = 48;
+        img.style.imageRendering = "pixelated";
+        img.style.borderRadius = "50%";
+        blockieEl.appendChild(img);
+    }
+
     const fromTitle = addressTitle(tx.from, state.wallets);
     const toTitle = addressTitle(tx.to, state.wallets);
     $("tx-detail-from").innerHTML = txAddressHtml(