fix: resolve code review issues — schema mismatch, test fixes, pop-out render

- Fix a2ui-format.md schema to match renderer: rename 'options' → 'filters' in
  filters block, replace 'active: boolean' with 'value: string' in filter options,
  update form select options from string[] to {label, value}[] objects (Critical #1)
- Fix 3 failing tests in test_researcher_agent.sh to use @mention paths without .md
  extension (Important #2)
- Complete pop-out feature in VisualBlock.handlePopOut() by posting render message
  to popup window after 500ms initialization delay (Important #3)
- Update test_context_files.sh to match new a2ui-format.md schema (filters array
  key check, value field check)

frontend/src/components/ChatPanel.tsx

@@ -76,6 +76,17 @@ function VisualBlock({
           w.document.open()
           w.document.write(html)
           w.document.close()
+          // Give the iframe time to initialize, then send the render message
+          setTimeout(() => {
+            w.postMessage(
+              {
+                jsonrpc: '2.0',
+                method: 'render',
+                params: { code: payload.code, data: payload.data ?? {} },
+              },
+              '*'
+            )
+          }, 500)
         })
         .catch(() => {
           w.close()