Fix ConditionalBlock crash in manuscript projects

In manuscript.lua, using pandoc.List() to build block collections and assigning to divEl.content changed the content type from "Blocks" to "List". When ConditionalBlock returned el.content, it returned a List without a .walk() method, causing crashes during AST traversal. Changed to pandoc.Blocks({}) to maintain proper type throughout the filter chain.

Fixes #13616

Author: cderv

src/resources/filters/layout/manuscript.lua

@@ -57,10 +57,10 @@ function manuscript()
         -- If this is a notebook embed cell, 'lift' the contents of any child divs
         -- up (unroll their contents), this will help us avoid
         -- labeling divs marked as `cells` more than once
-        local blocks = pandoc.List()
+        local blocks = pandoc.Blocks({})
         for _, childBlock in ipairs(divEl.content) do
           if is_regular_node(childBlock, "Div") then
-              tappend(blocks, childBlock.content)
+              blocks:extend(childBlock.content)
           else
             blocks:insert(childBlock)
           end