Badge centroids now read Vue Flow's live computedPosition instead of the
store, which commits positions only on drop — so badges no longer lag a
node drag. Centres use real node dimensions, dropping the hard-coded nudge.
Loops are derived from the wiring, never stored (ADR-0001): a signed
graph (link polarities plus flows' inherent inflow/outflow) is searched
with Tarjan SCC and a capped enumeration, classifying each cycle R or B
by the parity of its negative links. Both the result count and the
search are bounded so detection can never blow the frame budget.
