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/21-revenue_long.sql

@@ -1,5 +1,15 @@
+-- Revenue rows, classified by crosswalk MEMBERSHIP rather than item-code
+-- first letter (see 20-spending_long.sql for why prefixes cannot work).
+-- Scope is Census General Revenue: every crosswalk revenue subtype EXCEPT
+-- insurance_trust (Y01/Y02/Y04/Y11/Y12/Y51/Y52). Owner ruling 2026-07-30:
+-- the default revenue concept stays general; surfacing insurance-trust
+-- revenue through an explicit concept argument is uscogdata#12.
 CREATE OR REPLACE VIEW revenue_long AS
 SELECT *
 FROM long
-WHERE LEFT(item_code, 1) IN ('T', 'A', 'U', 'B', 'C', 'D')
+WHERE item_code IN (
+    SELECT item_code FROM summary_categories
+    WHERE category_type = 'revenue'
+      AND revenue_subtype <> 'insurance_trust'
+  )
   AND NOT is_aggregate;