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

man/cog_geographic_rollup.Rd

@@ -10,7 +10,7 @@ cog_geographic_rollup(
   years,
   per_capita = FALSE,
   adjust_to_year = NULL,
-  expenditure_concept = c("direct", "total"),
+  expenditure_concept = c("primary", "direct", "total"),
   coverage = c("all", "census", "consistent")
 )
 }
@@ -30,12 +30,12 @@ are excluded from the result.}
 
 \item{adjust_to_year}{Integer base year for CPI-U conversion, or `NULL`.}
 
-\item{expenditure_concept}{`"direct"` (default) or `"total"`. Currently only
-`"direct"` is accepted; the `"total"` option exists in [cog_spending()] for
-single-government queries but cannot be used here because combining Total
-across multiple layers of government double-counts intergovernmental
-transfers (a state's payment to a school district is the same dollar the
-district reports as its own Direct spending).}
+\item{expenditure_concept}{`"primary"` (default), `"direct"`, or
+`"total"` -- see [cog_spending()] for the three concepts. `"total"` is
+refused here because combining Total across multiple layers of
+government double-counts intergovernmental transfers (a state's payment
+to a school district is the same dollar the district reports as its own
+Direct spending); `"primary"` and `"direct"` combine safely.}
 
 \item{coverage}{How to handle the Census of Governments survey cycle,
   which is a **complete census only in years ending in 2 and 7** -- every