Suggest full serialization on feature-ai-rag: port the child-listing fix and drop the @components expansion

[reekitconcept]

The feature-ai-rag branch forked from main on 2026-07-12, before #106 (the fix for #105, merged 2026-08-10) landed on main. So on the feature branch serialize_brain() still runs the full serialization with neither include_items=False nor any expansion control:

• for folderish types every suggestion runs an extra catalog query and embeds the whole child listing (the original Suggest: full serialization of folderish types embeds the whole child listing in every suggestion #105 problem), and
• every fully serialized suggestion embeds the @components expansion links (breadcrumbs, navigation, actions...), which the suggest dropdown never follows — pointed out by @davisagli in the review of Suggest: do not embed the child listing of folderish suggestions (#105) #106: Suggest: do not embed the child listing of folderish suggestions (#105) #106 (review)

Fix, as two separate commits on the feature branch:

1. cherry-pick of the Suggest: do not embed the child listing of folderish suggestions (#105) #106 fix (include_items=False),
2. new: additionally pass include_expansion=False.

The commits stay separate on purpose: commit 2 is also cherry-picked to a small PR against main, so the @components fix makes the v2 release instead of waiting for the feature branch merge (which happens only after v2). No separate ticket for the main PR — it references this one and #105.