fix: address Task 3 code review (bool_or, invariant tests, guards, docs)

Nine review items on the expenditure_concept = direct|total feature:

- bool_and(is_aggregate) -> bool_or(is_aggregate) for aggregate_fallback:
  bool_and silently misreported $5,740,775,000 of aggregate-sourced IG
  dollars (AL state 2011) as aggregate_fallback = FALSE, because the dense
  wide-era data puts a $0 leaf row in the same group as the real aggregate
  row. bool_or is a no-op for Direct/Revenue (verified: 0 mismatched groups
  across both tables) and correct for the IG leg.
- Added a year-disjointness invariant test for the four legacy
  aggregate/leaf IG pairs (M47/M94, M89/M91-93, L47/L94, L89/L91-93),
  scoped to the aggregate flag rather than bare code presence (M89/L89
  continue past 2011 as independent, non-aggregate leaves).
- Extended the real-SQL-text/synthetic-parquet harness in test-views.R to
  pin ig_long/ig_long_harmonized's predicates directly (aggregate rows
  retained, NULL harmonized_code coalesced, L-- excluded), rather than
  relying on one fixture row's incidental shape.
- Added a test proving the .harmonization_view_files schema-v5 guard is
  necessary (not just incidental) against a corpus whose `long` genuinely
  lacks a harmonized_code column, and rewrote the misleading "v5-only
  parquet files" comment to name both real reasons a file is gated.
- Fixed an NA-fragile subtype filter, extended the expected-view-list
  test, guarded .verb_spendrev() against total on a non-spending
  view_base, added a roxygen caveat against summing total across levels
  of government, and replaced an uncheckable corpus-wide SQL comment
  figure with a fixture-verifiable one.

Full suite: 485/0/0 -> 503/0/0 (18 new expectations, zero pre-existing
value changed).

inst/sql/25-ig_long_harmonized.sql

@@ -2,9 +2,12 @@
 -- than harmonized_code alone: aggregate rows carry NO harmonized_code by
 -- construction (harmonized space is leaf-only), so a plain
 -- `harmonized_code IS NOT NULL` filter would drop every legacy IG aggregate --
--- 6.4e9 of M and 3.1e8 of L in corpus units. COALESCE keeps the one real IG
--- collapse rule (M38 -> M36, SB012, year-disjoint 1967-2011 vs 2012+) while
--- never dropping a row.
+-- in the bundled fixture corpus (year 2011; 2012+ all carry a harmonized_code)
+-- that is $379,016,063k across 25,688 M rows and $2,277,458k across 19,266 L
+-- rows (`SELECT year, LEFT(item_code,1), SUM(amt), COUNT(*) FROM ig_long
+-- 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.
 CREATE OR REPLACE VIEW ig_long_harmonized AS
 SELECT * REPLACE (COALESCE(harmonized_code, item_code) AS item_code)
 FROM long