feat: three-concept expenditure model classified by crosswalk membership (#11)

Rewrites expenditure/revenue classification off item-code first-letter
prefixes and onto summary_categories membership (F-018: prefix Y spans
revenue, expenditure, and balance codes), and exposes
expenditure_concept = c("primary", "direct", "total") with primary as
the new default:

  primary = operations + capital + assistance
  direct  = primary + interest + insurance_benefits   (Census Direct)
  total   = direct + intergovernmental                (M/L/Q via ig views)

- inst/sql: flow views (20-25) select by crosswalk membership;
  summary_categories moves to 11- so it registers before them (DuckDB
  binds view sources eagerly). The IG leg gains Q11/Q12/Q18 state
  school-system payments (F-017).
- R: one subtype scope per verb call drives the verb SQL, the
  harmonization exclusion count, and the complete = TRUE grid;
  flow_prefixes survives only to scope recipe suggestions.
  cog_geographic_rollup/cog_peer_compare accept primary|direct, still
  refuse total, and now actually pass the concept through.
- Balance codes can never reach a spending or revenue result
  (uscogdata#25), asserted at both view and verb level.
- Deletes the #11 skip; per the 2026-07-30 owner ruling the F-018 Y01
  proof is asserted against the crosswalk, not the default
  cog_revenue() call (which stays General Revenue pending #12).

Suite: 696 pass / 0 fail / 1 skip (#12, expected).

Closes #11

R/revenue.R

@@ -18,6 +18,10 @@ cog_revenue <- function(govid, years, category = NULL,
                         per_capita = FALSE, adjust_to_year = NULL,
                         basis = c("harmonized", "raw"), recipe = NULL,
                         complete = FALSE) {
+  # flow_prefixes no longer classifies rows (crosswalk revenue_subtype
+  # membership does -- General Revenue, i.e. everything except
+  # insurance_trust) -- it only scopes the recipe-suggestion machinery to
+  # this verb's recipe families (see R/suggestions.R).
   .verb_spendrev(
     verb           = "cog_revenue",
     view_base      = "revenue_annotated",