feat: cog_recipes + recipe= + signposting suggestions

Adds cog_recipes() to list the curated harmonization_recipes catalog (24
recipes / schema_version >= 5), and a recipe= argument on cog_spending()/
cog_revenue() that runs a recipe's generic multi-code join instead of the
category view: SUM(amt * weight) across whichever component codes are
present for a (year, canonical_govid), scoped by gov_type_scope. The join
deliberately does not filter is_aggregate -- the wide era (<= 2011) exposes
these split families (corrections 04+05, IG *89/*47, U4- rents, etc.) ONLY
as aggregate rows, with leaf codes first appearing in 2012, so excluding
aggregates would zero out the wide-era half of every recipe. This is safe
by corpus construction: wide-era rows are aggregate-only, modern rows are
leaf-only, and every component is year-scoped, so there is no
double-counting. recipe= is mutually exclusive with category=; the result's
subtype column reads "recipe" and category reads the recipe's label.

Adds recipe-component-driven signposting: when a basis="harmonized" +
category query comes back with zero rows in a requested year, and a
harmonization recipe covering that category would actually produce rows
for this government in that year (via the same join .run_recipe() uses),
the recipe is surfaced in provenance$suggestions plus one
cli::cli_inform() message. This is deliberately keyed off recipe
components rather than harmonization_map's suggested_recipe_id column
(which is empty on every live row -- the wide era's split families are
NA-by-construction via aggregate exclusion, not an NA ruling to hang a
suggestion off of).

Also populates the previously-always-empty provenance$series_break_refs
(schema v5 only: series_breaks_pq rows whose fin_code is among the
observed codes and whose break_year falls in the requested span), and
extends cog_explain() with Basis/Harmonization/Recipe/Suggestions/Series
breaks sections.

tests/testthat/test-spending.R

@@ -292,6 +292,21 @@ test_that("v4 corpus: explicit basis = 'harmonized' aborts", {
   })
 })
 
+test_that("provenance$series_break_refs is a populated-when-applicable character vector", {
+  skip_if_no_corpus()
+  with_fixture_corpus({
+    r <- cog_spending("121011212191", 2020L, "Corrections")
+    refs <- attr(r, "provenance")$series_break_refs
+    expect_type(refs, "character")
+    # No catalogued series_breaks_pq row falls inside this fixture's
+    # 2011/2012/2019/2020 window for the codes this query touches (E04/G04)
+    # -- data-verified; the mechanism itself is what's under test here, via
+    # a query-shaped unit test in test-views.R since the fixture has no
+    # positive case to pin against.
+    expect_equal(refs, character(0))
+  })
+})
+
 test_that("v4 corpus: explicit basis = 'raw' still works", {
   skip_if_no_corpus()
   with_doctored_schema_version(4L, {