Adds the NEWS entry, a Financial data pkgdown reference section (none
existed for cog_spending/cog_revenue), and corrects CLAUDE.md's SQL-layer
claim, view count, test count and fixture-year description against
measured values. Also documents balance_caveats in
inst/schemas/provenance-v1.json (test-first: added a schema-documentation
test to test-balances.R, confirmed it failed, then fixed the schema) and
fleshes out cog_balances()'s @return roxygen to enumerate its conditional
columns, regenerating man/cog_balances.Rd.