fix(e2e): fix 27 E2E test failures across 3 spec files

Fix stale v2 CSS selectors for v3 UI, WebKit2GTK keyboard/focus
quirks (JS-dispatched KeyboardEvent, programmatic focus check,
backdrop click close), conditional render timing (waitUntil for
project boxes, null handling for burn-rate/cost elements), and
AgentPane missing closing > on data-testid div tag.

v2/src/lib/components/Agent/AgentPane.svelte

@@ -375,7 +375,7 @@
   });
 </script>
 
-<div class="agent-pane" data-testid="agent-pane" data-agent-status={session?.status ?? 'idle'}
+<div class="agent-pane" data-testid="agent-pane" data-agent-status={session?.status ?? 'idle'}>
   {#if parentSession}
     <div class="parent-link">
       <span class="parent-badge">SUB</span>