Fix the report's transfer rows rendering as text

The report builds its excluded rows as a group per currency -- the
transfer legs and, when a tolerance admitted one, the fee -- so its tbody
children nest two arrays deep. h flattened only one level, so each group
was stringified and the page showed "[object HTMLTableRowElement]" wherever
a period held a matched transfer. Children now flatten all the way down.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

internal/web/static/app.js

@@ -41,7 +41,9 @@ function blankTransfer() {
 // --- plumbing -------------------------------------------------------------
 
 // h builds an element. Text always goes in as a text node, never as HTML,
-// since descriptions come straight off bank statements.
+// since descriptions come straight off bank statements. Children flatten all
+// the way down: a map that yields a group of rows — the report's transfers
+// and their fee — would otherwise be stringified into the page.
 function h(tag, attrs, ...children) {
   const el = document.createElement(tag);
   for (const [k, v] of Object.entries(attrs || {})) {
@@ -51,7 +53,7 @@ function h(tag, attrs, ...children) {
     else if (k === 'value') el.value = v;
     else el.setAttribute(k, v === true ? '' : v);
   }
-  for (const c of children.flat()) {
+  for (const c of children.flat(Infinity)) {
     if (c === null || c === undefined || c === false) continue;
     el.append(c instanceof Node ? c : document.createTextNode(String(c)));
   }