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

inst/sql/24-ig_long.sql

@@ -1,4 +1,6 @@
--- Intergovernmental expenditure rows (M = to local govts, L = to state govts).
+-- Intergovernmental expenditure rows: crosswalk spend_subtype =
+-- 'intergovernmental' (M = to local govts, L = to state govts, Q11/Q12/Q18
+-- = state payments to school systems -- uscogdata#11, finding F-017).
 --
 -- Deliberately does NOT filter `NOT is_aggregate`, unlike spending_long. In the
 -- wide era (<= FY2011) the IG families M05/M12/M47/M89/L47/L89 are published
@@ -9,10 +11,15 @@
 -- from 2012 alongside M91-93), so no row is ever counted twice. Same argument
 -- the pipeline's recipe joins use.
 --
--- `L--` IS excluded: it is the IG-to-state FAMILY TOTAL and genuinely rolls up
--- the L-NN codes, so including it would double-count.
+-- `L--` stays excluded: it is the IG-to-state FAMILY TOTAL and genuinely
+-- rolls up the L-NN codes, so including it would double-count. The crosswalk
+-- deliberately carries no `--` family-total codes, so membership excludes it
+-- (guarded by "the IG leg never includes the L-- family total" in
+-- tests/testthat/test-expenditure-concept.R).
 CREATE OR REPLACE VIEW ig_long AS
 SELECT *
 FROM long
-WHERE LEFT(item_code, 1) IN ('M', 'L')
-  AND item_code NOT LIKE '%--';
+WHERE item_code IN (
+    SELECT item_code FROM summary_categories
+    WHERE spend_subtype = 'intergovernmental'
+  );