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.

R/series_breaks.R

@@ -0,0 +1,22 @@
+# R/series_breaks.R
+# Populates prov$series_break_refs (schema in inst/schemas/provenance-v1.json
+# defines the field; it was always present but always empty pre-Phase-R2)
+# with the ids of any catalogued series break whose fin_code appears among
+# the result's observed item codes and whose break_year falls inside the
+# requested year span -- the "break warnings in the provenance envelope"
+# spec § 5 promises downstream consumers (cog-api passes provenance through
+# verbatim). schema_version >= 5 only: series_breaks_pq isn't registered on
+# an older corpus.
+
+#' @noRd
+.build_series_break_refs <- function(con, codes_observed, years, schema_version) {
+  if (schema_version < 5L || length(codes_observed) == 0L) return(character(0))
+  sql <- sprintf(
+    "SELECT DISTINCT break_id
+     FROM series_breaks_pq
+     WHERE fin_code IN (%s) AND break_year BETWEEN %d AND %d
+     ORDER BY break_id",
+    .sql_lit_chr(codes_observed), min(as.integer(years)), max(as.integer(years))
+  )
+  DBI::dbGetQuery(con, sql)$break_id
+}