Flag Document Selection As Decision

Decision Pulse §5.1's "flag any... doc line as a decision" — the same quick-capture shortcut as routers/context.py's chat-message counterpart (db_decisions.create, provenanced via a references context_link rather than a new column). quote is the selected text (same {from, to, quote} selection the "+ Comment" button already captures in DocEditor.tsx's SelectionCommentButton) — used as the decision's context, not stored as a precise anchor, since Pulse's flagging is a fast-capture shortcut, not Extraction's receipt system.