fix: govid input ergonomics + clearer missing-govid message

Two UX fixes surfaced by first real-user use:

1. cog_spending / cog_revenue / cog_geographic_rollup now accept either
   a character vector OR a data.frame with a canonical_govid column
   (e.g. output of cog_gov_search() or cog_find_peers()). Shared
   .coerce_govid_input() helper in session.R. This lets the natural
   pipe work:

     cog_gov_search('MIAMI', state='FL', type='city') |>
       cog_spending(years=2022, category='Police')

   cog_peer_compare already accepted a data.frame for the peer arg;
   behavior there is unchanged.

2. .check_govids_in_scope() message reworded. The old text led with
   'v0.1 covers gov_types 0-3' which falsely implied the missing govids
   were scope-excluded types when the more common real cause is a typo
   or a guessed value. New message leads with typo + pre-2017 PID,
   mentions scope exclusion as one possibility, and points at
   cog_gov_search() as the recovery path.

Tests: 165 pass / 0 fail. check 0E/0W/0N.

tests/testthat/test-rollup.R

@@ -78,6 +78,18 @@ test_that("cog_geographic_rollup provenance reports the outer verb", {
   expect_true(grepl("cog_geographic_rollup", prov$call))
 })
 
+test_that("cog_geographic_rollup accepts data.frames per layer", {
+  skip_if_no_corpus()
+  fl_state  <- cog_gov_search("^FLORIDA STATE GOVT$", type = "state")
+  broward   <- cog_gov_search("^BROWARD COUNTY$", state = "FL", type = "county")
+  r <- cog_geographic_rollup(
+    govids = list(state = fl_state, county = broward),
+    category = "Police", years = 2020L
+  )
+  expect_setequal(unique(r$layer), c("state", "county"))
+  expect_gt(nrow(r), 0L)
+})
+
 test_that("cog_geographic_rollup rejects invalid inputs", {
   expect_error(cog_geographic_rollup(list(), "Police", 2020L), "length")
   expect_error(cog_geographic_rollup(c("101006006"), "Police", 2020L), "list")