fix: surface ALL-scoped series breaks in provenance (#19)

.build_series_break_refs() matches `fin_code IN (<codes in the result>)`.
No row's item_code is ever the literal "ALL", so the four corpus-wide
entries could never match and reached no user:

  SB085  1977  dollar precision across the 1976/1977 boundary
  SB087  2002  imputation exclusion FY2002-2006
  SB194  2012  dense -> sparse representation change
  SB086  2017  government id scheme change

SB194 is why this matters now. cog_pipeline#64 DoD 4 was "series_breaks.csv
carries an ALL @ 2012 entry describing the representation change, SO
cog_explain() surfaces it". The entry shipped; the reader dropped it. A
query spanning FY2011 -> FY2012 crosses the boundary where an absent cell
stops meaning "Census published $0" and starts meaning "not reported", and
nothing said so.

Provenance gains `corpus_break_refs`, built by .build_corpus_break_refs()
on the break_year window alone -- which codes a result happens to contain
is irrelevant to a caveat about the corpus. A separate field rather than
more entries in series_break_refs, because an ALL caveat qualifies the
whole result and folding the two together invites reading it as a caveat
about one series; .build_series_break_refs() now excludes 'ALL' explicitly
so the two stay disjoint by construction. cog_explain() prints them under
their own "Corpus-wide caveats" heading, and cog-api passes provenance
through verbatim, so the field reaches the API with no change there.

On the year rule: all four entries are BOUNDARY caveats -- their own
join_advice speaks of crossing 1976/1977, of FY2002-2006, of absence not
being comparable across FY2012, of pre- vs post-2017 ids -- so the same
`break_year BETWEEN min(years) AND max(years)` rule the code-specific path
uses is the right one, and matches the issue's DoD 1. The issue's DoD 3
also asks that a FY2011 query surface SB085; that cannot hold under DoD 1
and does not hold under any reading of SB085's text, whose boundary is
1976/1977. Tested with a range that actually spans it, and flagged on the
issue.

Stacked on fix/regen-fixture-corpus-18: SB194 does not exist in main's
bundled fixture, which predates the break being catalogued.

Suite: 606 pass / 0 fail / 6 skip (was 594/0/6).
cog-api 357 / 0 / 8, unchanged.

R/provenance.R

@@ -37,11 +37,20 @@
 
   schema_version <- suppressWarnings(as.integer(manifest$schema_version %||% 0L))
   con <- .uscogdata_env$con
-  break_refs <- if (!is.null(con) && DBI::dbIsValid(con)) {
+  have_con <- !is.null(con) && DBI::dbIsValid(con)
+  break_refs <- if (have_con) {
     .build_series_break_refs(con, codes_observed, years, schema_version)
   } else {
     character(0)
   }
+  # Corpus-wide caveats travel separately: they qualify the whole result
+  # rather than one series, and they do not depend on codes_observed (see
+  # .build_corpus_break_refs()).
+  corpus_refs <- if (have_con) {
+    .build_corpus_break_refs(con, years, schema_version)
+  } else {
+    character(0)
+  }
 
   list(
     verb = verb,
@@ -116,6 +125,7 @@
       )
     ),
     series_break_refs = break_refs,
+    corpus_break_refs = corpus_refs,
     manifest = list(
       schema_version = as.integer(manifest$schema_version),
       pipeline_commit = manifest$pipeline_commit %||% NA_character_,