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)

tests/test_context_files.sh

@@ -60,12 +60,12 @@ check_contains "$A2UI" "a2ui fenced code block" '```a2ui'
 echo ""
 echo "=== Checking a2ui-format.md: block type 'filters' ==="
 check_contains "$A2UI" "filters type" '"type": "filters"'
-check_contains "$A2UI" "filters options array" '"options"'
+check_contains "$A2UI" "filters array key" '"filters"'
 check_contains "$A2UI" "Toyota option" '"Toyota"'
 check_contains "$A2UI" "Honda option" '"Honda"'
 check_contains "$A2UI" "Hyundai option" '"Hyundai"'
 check_contains "$A2UI" "Under \$5K option" '"Under $5K"'
-check_contains "$A2UI" "active field" '"active"'
+check_contains "$A2UI" "value field" '"value"'
 
 echo ""
 echo "=== Checking a2ui-format.md: block type 'table' ==="