Recursive renderer for <cngx-filter-builder>. Owns the slot-cascade
machinery for every per-row visible region (addFilterButton,
addGroupButton, removeButton, logicToggle, negationToggle,
expressionTemplate, groupTemplate) plus path-keyed context caches.
Internal - not exported through public-api.ts. The host component
(CngxFilterBuilder) mounts this body directly; state-driven UI
(loading / error / refreshing) is the consumer's concern (wrap with
<cngx-async-container [state]>). The body lifts behind
CNGX_FILTER_BUILDER_BODY_HOST so consumers can swap the recursive
renderer without forking the shell.