fix: literal name search, units docs, peer-summary semantics (#16, #15, #14)

The three kodor/fix issues, taken over after a day with no branch, PR or
comment on any of them. Batched because each is single-file with a committed
acceptance test, and two share documentation surfaces.

#16 (F-025) -- cog_gov_search() utility mode interpolated `name` straight
into regexp_matches() unescaped, while basket mode in the same file already
routed it through .escape_regex() with the comment "so `name` is treated as
a literal substring". Two failure modes, both HTTP 200 through the API:
a government could not be found by its own complete name when that name
contains a metacharacter (FREDONIA (BRISCOE) CITY returned nothing), and a
bare "." matched all 608 Wisconsin cities. Malformed pattern text reached
the engine as an error, which cog-api surfaced as a 500 -- reachable by
typing a real name one character at a time ("Athens-Clarke County (bal").

Utility mode now calls the escaper that already existed. Roxygen updated:
utility mode is documented as a literal case-insensitive substring match,
and the basket-mode "substring fallback" step no longer describes itself as
a regex either.

  BEHAVIOUR CHANGE worth flagging: anchored exact-match searches stop
  working, because there is no regex left to anchor. Two existing tests used
  "^BROWARD COUNTY$" and "^FLORIDA$" as their exact-match idiom; both now
  search for those characters literally. Updated to the bare names, which
  still resolve to exactly one row each once scoped by state/type (verified,
  not assumed). There is no exact-match option in utility mode any more --
  noted on the issue, since that is a real if small capability loss.

#15 (F-004) -- the raw Census files report thousands of dollars; this
package multiplies by 1000 and returns full US dollars. Correct, and already
stated in ?cog_spending / ?cog_revenue @return, in provenance, and in
cog-api's data-dictionary. Absent from every surface a reader meets FIRST.
Added to README.md as its own section and to both vignettes' openings.

The dangerous one is cog_explorer/CLAUDE.md, which states the opposite rule
("All raw `amt` values are in $1,000s") without scoping it to the raw column
-- a reader applying that to amt_nominal overstates by 1000x and gets a
plausible-looking number rather than an obvious error. Fixed there too; that
directory has no git remote, so it rides in no PR and is left uncommitted
for the owner.

#14 (F-021) -- .peer_summary_rows() computes stats::quantile() separately
inside each (year, spend_subtype, category) cell, so a summary_p50 row is
"the median peer's value in that one category", never "the value of the
median peer's total" -- the median peer for Police and for Fire are usually
different governments. Summing them across categories misstated a
total-spending band by -32.7% to +251.0% across 24 years, with a sign flip
at FY2012. The verb is right and its documented use (facet by role AND
category) is unaffected, so the fix is @return prose plus a worked snippet
showing the correct computation: sum each peer's own categories first, then
take the quantile of those per-government totals.

This is the R-side counterpart of cog-api#9, fixed on the API surface
earlier today; the wording is deliberately consistent across the two.

Note the phrase "not additive" has to stay on one roxygen source line --
the test greps the generated Rd, where a line wrap turns it into
"not   additive" and stops matching. Cost one red run to find.

man/ regenerated with roxygen 8.0.0 against a repo built with 7.3.3, so
cog_spending.Rd and DESCRIPTION were reverted -- their entire diff was
version churn (reindentation, RoxygenNote -> Config/roxygen2/version) with
no content change. The two Rd files kept carry only the edits above.

Suite: 629 pass / 0 fail / 3 skip (was 606/0/6). The three remaining skips
are #11, #12 and #13.

README.md

@@ -19,6 +19,27 @@ package implements.
 # pak::pkg_install("gitea.civilytics.org/Civilytics/uscogdata")
 ```
 
+## Amounts are in full US dollars
+
+Every amount column this package returns — `amt_nominal`, `amt_real`,
+`amt_per_capita_nominal`, `amt_per_capita_real` — is in **full US dollars**.
+
+The raw Census source files report **thousands of dollars**, and the corpus's
+own `amt` column preserves that. The verbs multiply by 1000 on the way out, so
+you never have to. The conversion is recorded in every result:
+
+```r
+r <- cog_spending("552025209777", 2020L)
+attr(r, "provenance")$transformations$units_conversion
+#> $applied TRUE  $source_unit "$1,000s (raw Census)"  $target_unit "$USD"  $multiplier 1000
+```
+
+**Do not multiply again.** If you have read elsewhere that COG amounts are in
+`$1,000s` — true of the raw corpus, and of `cog_explorer`'s conventions doc —
+that rule does not apply to anything a `cog_*()` verb hands you. Applying it
+twice overstates every figure by 1000x, and the result looks plausible rather
+than obviously wrong.
+
 ## Configuration
 
 - `USCOGDATA_URL` — corpus root URL (public Nextcloud share, trailing slash)