B3 (right-click) on a word now plumbs it directly without visually
selecting it first. Double-click word selection includes underscores,
so snake_case selects the whole identifier.
Extract selectBracketPair, selectWordAt, and helpers into TextSelection.js
and import it in both ChatBlockDelegate.qml and ChatPane.qml. Prompt
textarea now has the same double-click behavior as chat blocks:
delimiter adjacent to cursor -> select pair content, else -> word select.
Quotes use parity to decide direction and scan document-wide, so
multi-line content between the pair is selected in full.
Levi Neely