Fix tx amount display to 4 decimal places, add relative time to tx detail

- Transaction values now use exactly 4 decimal places (was 6),
  matching balance display everywhere else
- Transaction detail view shows "2026-02-25 15:04:23 (23 days ago)"
  instead of just the ISO date
- Added Display Consistency policy to README

src/popup/views/addressDetail.js

@@ -131,7 +131,8 @@ function showTxDetail(tx) {
     $("tx-detail-from").textContent = tx.from;
     $("tx-detail-to").textContent = tx.to;
     $("tx-detail-value").textContent = tx.value + " " + tx.symbol;
-    $("tx-detail-time").textContent = isoDate(tx.timestamp);
+    $("tx-detail-time").textContent =
+        isoDate(tx.timestamp) + " (" + timeAgo(tx.timestamp) + ")";
     $("tx-detail-status").textContent = tx.isError ? "Failed" : "Success";
     showView("transaction");
 }