Aggregate the canonical lake over chosen dimensions (spine, entity, period, currency, method, version, grain, fx_state)

Aggregate the canonical lake over chosen dimensions (spine, entity, period, currency, method, version, grain, fx_state). Returns sums plus a basis verdict. Aggregates ONLY — the lake holds far more lines than belong in a context window, and a sum answers almost every question a row dump would. Undeclared source codes appear as spine="unmapped" and are never folded into a node: if that row is present, the other totals are incomplete and must be reported as such.