docs: correct coverage_window scope and the stale CLAUDE.md Current State block (#25)

F-7: inst/schemas/provenance-v1.json described coverage_window as mapping
each *observed* balance_subtype, but the query at R/balance_caveats.R has
no predicate tied to the query's codes and always returns every subtype in
the mounted corpus. Took option (b) of the two the review offered -- change
the doc, not the code. Reporting all windows is the better product
behaviour (it answers 'is there a family I missed?'), it is what cog-api#26
already forwards verbatim, and option (a) would make the block empty for a
0-row result. Reworded to say the windows are corpus-wide and that
'truncated' is the query-scoped field. Pinned by a new test either way.

F-10: the 'Current State' block was self-contradictory after a partial
update -- headed 2026-04-27, claiming branch main @ d65e9fe, with a
2026-08-03 test count measured on feat/cog-balances-25 underneath it, and
listing README.md / _pkgdown.yml as outstanding when both exist and
_pkgdown.yml was edited by this branch. All numbers below re-measured on
the final tree after every other fix in this wave, not before:
788 tests (testthat::test_local()), 14 exports (NAMESPACE), 14 man/*.Rd,
2 vignettes, no docs/ (pkgdown::build_site() genuinely still outstanding,
as is the .Rbuildignore fixture entry -- both kept in the list).

The related deferred README.md item is closed with no change, per the
review's ruling: README.md enumerates no verbs at all, so naming
cog_balances would make it the only non-cog_spending verb mentioned.

inst/schemas/provenance-v1.json

@@ -55,7 +55,7 @@
     },
     "balance_caveats": {
       "type": ["object", "null"],
-      "description": "Present only on cog_balances() results (null/absent for cog_spending()/cog_revenue()). `not_gaap` is always TRUE and `not_gaap_note` explains that Census holdings are gross -- no liabilities are netted -- so they are NOT comparable to a GAAP fund balance. `coverage_window` maps each observed balance_subtype to its measured [min year, max year] in the mounted corpus (never hardcoded). `truncated` lists the subtypes whose coverage_window does not fully span the requested years.",
+      "description": "Present only on cog_balances() results (null/absent for cog_spending()/cog_revenue()). `not_gaap` is always TRUE and `not_gaap_note` explains that Census holdings are gross -- no liabilities are netted -- so they are NOT comparable to a GAAP fund balance. `coverage_window` maps EVERY balance_subtype present in the mounted corpus -- not only the ones this query observed -- to its measured [min year, max year] there (never hardcoded), so a caller can see which families exist and over what span before deciding they missed one. `truncated` is the query-scoped field: it lists only the subtypes this result actually observed whose coverage_window does not fully span the requested years.",
       "properties": {
         "not_gaap": { "type": "boolean" },
         "not_gaap_note": { "type": "string" },