feat: revenue_concept = c("general", "total") off the crosswalk (#12)

Closes the last blocked test in the suite. Owner ruled both halves of the
open question yes on 2026-07-30.

`cog_revenue()` gains `revenue_concept`, mirroring `expenditure_concept`,
with Census's two published concepts defined as crosswalk
`revenue_subtype` sets rather than item-code prefixes:

  general = own_source + federal + state + local_aid   (the default)
  total   = general + utility + liquor_store + insurance_trust

The manual defines the first by subtracting the other three from the
second (4.3), so both are computable only once all four families are
named -- which cog_pipeline#79 does. Insurance trust now includes the
employee-retirement X codes (X01/X02/X05/X08) alongside the Y codes.

- inst/sql: revenue_long / revenue_long_harmonized carry EVERY revenue
  subtype; the concept narrows in R via the existing subtype_scope
  machinery, exactly as expenditure_concept narrows spending_long.
- cog_explain() now prints each verb's OWN concept. It previously
  printed `expenditure_concept` unconditionally, so a cog_revenue()
  caller was told "Concept: primary" -- a spending concept their result
  has nothing to do with.
- Fixture regenerated at pipeline_commit aadb46b (330 crosswalk rows).

Corrected two stale expectations in the blocked test while un-skipping
it. It asserted X01+X04+X05+X08 and omitted X02, which applies to state
governments and is nonzero for Wisconsin; X04 is an exhibit code for an
INTRAgovernmental transfer that Census's own "Total Emp Ret Rev"
excludes. Verified against that Census field: the right set is
X01+X02+X05+X08 = $2,283,883k, exactly. And its expected `total` of
$33,377,093k predated the Y codes being classified -- complete Total
Revenue for WI FY2012 is $34,881,961k (general 31,338,293 + Y 1,259,785
+ X 2,283,883).

Behaviour change worth knowing: `general` is now STRICT Census General
Revenue, so utility and liquor store revenue leave the default. Measured
on the fixture that is 15.9% of what cog_revenue() returned for cities,
vs 1.2% for states and 1.7% for counties.

Suite: 716 pass / 0 fail / 0 skip -- the first time this package has had
no skipped tests.

Closes #12

README.md

@@ -71,6 +71,38 @@ enforce this by refusing `expenditure_concept = "total"`. See
 `vignette("total-spending", package = "uscogdata")` for the full
 explanation with worked examples.
 
+## General vs Total revenue
+
+`cog_revenue(..., revenue_concept = c("general", "total"))` selects between
+Census's two published revenue concepts, again defined as crosswalk
+`revenue_subtype` sets rather than item-code prefixes:
+
+- `"general"` (the default) is Census **General Revenue**: own-source
+  (taxes, charges, miscellaneous) plus federal, state and local
+  intergovernmental aid.
+- `"total"` is Census **Total Revenue**: `general` plus utility revenue
+  (`A91`–`A94`), liquor store revenue (`A90`), and insurance trust revenue
+  (unemployment and workers' compensation `Y` codes plus the
+  employee-retirement `X` codes).
+
+The manual defines the first by subtracting the other three from the second,
+so the two are related by Census's own identity:
+
+```
+Total Revenue = General + Utility + Liquor Store + Insurance Trust
+```
+
+Two things worth knowing before switching to `"total"`:
+
+- **Utility revenue is large for cities.** Measured on the bundled fixture,
+  utility plus liquor store revenue is 15.9% of city (type 2) revenue, versus
+  1.2% for states and 1.7% for counties. `general` excludes it by definition.
+- **The employee-retirement (`X`) codes stop at FY2016**, when those systems
+  moved out of the annual finance file into the separate Annual Survey of
+  Public Pensions. A `"total"` series therefore steps down at the
+  FY2016/FY2017 seam for reasons of collection scope, not revenue (series
+  breaks `SB197`–`SB202`, in the corpus's `series_breaks` table).
+
 ## Developer notes
 
 ### Testing