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/25-ig_long_harmonized.sql

@@ -8,8 +8,15 @@
 -- WHERE harmonized_code IS NULL GROUP BY 1, 2`). COALESCE keeps the one real
 -- IG collapse rule (M38 -> M36, SB012, year-disjoint 1967-2011 vs 2012+)
 -- while never dropping a row.
+--
+-- Membership is checked on the published item_code (mirroring 24-ig_long.sql)
+-- rather than the COALESCEd code: every IG harmonization target (M36) is
+-- itself an IG crosswalk member, so the two are equivalent, and item_code is
+-- the column that exists on every row.
 CREATE OR REPLACE VIEW ig_long_harmonized AS
 SELECT * REPLACE (COALESCE(harmonized_code, item_code) AS item_code)
 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'
+  );