Frontend: complete task list (C1–L4), security, a11y, L1 block card helper

- React: response.ok checks (address, transaction, search); block number validation; stable Table keys; API modules (addresses, transactions, blocks normalizer)
- SPA: escapeHtml/safe URLs/onclick; getRpcUrl in rpcCall; cancel blocks rAF on view change; named constants; hash route decode
- SPA: createBlockCardHtml + normalizeBlockDisplay (L1); DEBUG console gating; aria-live for errors; token/block/tx detail escaping
- Docs: FRONTEND_REVIEW.md, FRONTEND_TASKS_AND_REVIEW.md; favicons; .gitignore *.tsbuildinfo

Co-authored-by: Cursor <cursoragent@cursor.com>

frontend/public/icon.svg

@@ -0,0 +1,14 @@
+<svg xmlns="http://www.w3.org/2000/svg" viewBox="0 0 64 64" width="64" height="64">
+  <defs>
+    <linearGradient id="bg" x1="0%" y1="0%" x2="100%" y2="100%">
+      <stop offset="0%" style="stop-color:#667eea"/>
+      <stop offset="100%" style="stop-color:#764ba2"/>
+    </linearGradient>
+  </defs>
+  <rect width="64" height="64" rx="12" fill="url(#bg)"/>
+  <!-- Magnifying glass (scout) -->
+  <circle cx="28" cy="28" r="14" fill="none" stroke="white" stroke-width="4"/>
+  <line x1="38" y1="38" x2="50" y2="50" stroke="white" stroke-width="4" stroke-linecap="round"/>
+  <!-- Small block link accent -->
+  <rect x="12" y="44" width="10" height="10" rx="2" fill="rgba(255,255,255,0.5)"/>
+</svg>