docs: fix stale test count and phantom notes column in cog_balances docs (#25)

Re-measured CLAUDE.md's test count on the final tree (764, not 763 --
the earlier number predated the balance_caveats schema test). Removed
notes from cog_balances()'s @return block: it was copied from
cog_spending()'s @return style without checking cog_balances() never
calls .verb_spendrev(), the only place that sets notes. Verified the
remaining documented columns against colnames() observed across every
argument combination (bare, per_capita, adjust_to_year, both, recipe,
category filter).

R/balances.R

@@ -42,10 +42,10 @@
 #'   wide era to the modern one.
 #'
 #' @return Tibble with columns `year`, `canonical_govid`, `gov_name`,
-#'   `balance_subtype`, `category`, `amt_nominal`, optional
-#'   `amt_per_capita_nominal` and `pop_source` (when `per_capita = TRUE`),
-#'   optional `amt_real` and `amt_per_capita_real` (when `adjust_to_year` is
-#'   set), `codes_included`, `aggregate_fallback`, `notes`. Amounts are full
+#'   `balance_subtype`, `category`, `amt_nominal`, `codes_included`,
+#'   `aggregate_fallback`, plus optional `amt_per_capita_nominal` and
+#'   `pop_source` (when `per_capita = TRUE`), and optional `amt_real` and
+#'   `amt_per_capita_real` (when `adjust_to_year` is set). Amounts are full
 #'   US dollars.
 #'
 #'   Carries a `provenance` attribute matching