Surface the requesting party on the decision overview

The single-memo review page already fetched and labeled
approval-engine's binding.principal "Requesting party" -- the party
the approval was issued on behalf of, distinct from memo.binding.principal
(the reviewer being bound). The overview/list page fetched the same
live approval record for status but never surfaced this field.

OverviewRow gains requesting_party, populated only when the fetched
binding's digest matches the memo's pinned digest (same trust
condition status already uses); ui.py renders it as "Requested by: ...".
No new approval-engine call or flex-auth scope needed -- the record was
already being read.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

Assistant: claude-code
Assistant-Model: sonnet
Assistant-Process: 169987@bnt-lap001
Assistant-Session: 322ef1ef-9048-4021-8570-b6d6f6347999

informed_decision/ui.py

@@ -148,6 +148,8 @@ def _overview_row(row):
         return (f'<div class="record"><strong>{text(row.memo_id)}</strong>'
                 f'<p class="muted">{text(reason)}</p></div>')
     facts = [f'Memo {text(row.memo_id)} · version {row.version}']
+    if row.requesting_party:
+        facts.append(f'Requested by: {text(row.requesting_party)}')
     if row.engine_status:
         facts.append(f'Approval status: {text(row.engine_status)}')
     elif row.reason: