fix(suggestions): scope candidate recipes by category_type (#34)

.query_candidate_recipes() (extracted in #33) now filters candidates by
category_type ('expenditure' vs 'revenue'), derived from the calling
verb's own flow_prefixes (E/F/G -> 'expenditure', else 'revenue').

Without this, a category shared across both flow families in
summary_categories leaked cross-family recipes: cog_revenue(category =
"Corrections") surfaced the expenditure-only corrections_combined recipe
(E04/E05) merely because "Corrections" is also a spending category name,
and cog_spending(category = "IG Federal") surfaced the revenue-only
ig_federal_b47_wide recipe. Both are wrong: following either hint would
attribute dollars to the wrong flow, or (IG Federal) fire the
coverage-gap machinery for a category the calling verb structurally
cannot report on at all.

Updates the two tests this changes the expected behavior of:
- "a mis-scoped cog_spending() call never attaches an M/L counterpart to
  a revenue-flavored recipe" (test-expenditure-concept.R): IG Federal is
  revenue-only, so a spending call now finds zero candidates outright
  rather than firing the suggestion and then blocking its M/L
  counterpart as a second-order check.
- "cog_revenue never suggests expenditure-only recipes"
  (test-recipes.R, was "I1: ... never fabricates suppressed dollars"):
  corrections_combined is expenditure-only, so a revenue call now never
  considers it as a candidate, rather than considering it and reporting
  zero suppressed dollars.

All 1078 tests pass (2 skipped live-corpus), measured devtools::test()
against this commit in a clean worktree stacked on the #33 refactor.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

tests/testthat/test-expenditure-concept.R

@@ -315,15 +315,17 @@ test_that("a mis-scoped cog_spending() call never attaches an M/L counterpart to
   # (SB194, cog_pipeline#64), so the recipe stopped being a candidate there.
   # FL state carries a real FY2011 B47 amount, so this exercises the guard
   # against a suggestion that genuinely fires.
+  #
+  # Issue #34: "IG Federal" maps to B-prefixed codes in summary_categories
+  # with category_type = 'revenue'. A spending verb (flow_prefixes E/F/G)
+  # now scopes its candidate query by category_type = 'expenditure', so it
+  # correctly finds NO candidates for this revenue-only category -- the
+  # suggestion machinery cannot fire, and no M/L counterpart is attached.
   r <- suppressMessages(
     cog_spending("120000226351", years = c(2005, 2011), category = "IG Federal")
   )
   sugg <- attr(r, "provenance")$suggestions
-  expect_gt(length(sugg), 0L)
-  ids <- vapply(sugg, function(s) s$recipe_id %||% "", character(1))
-  expect_true("ig_federal_b47_wide" %in% ids)
-  ig <- unlist(lapply(sugg, function(s) s$ig_recipe_id))
-  expect_length(ig, 0L)
+  expect_length(sugg, 0L)
 })
 
 test_that("C1: 'total' on a legacy aggregate-only family reports the IG-only figure honestly, not as Direct + IG", {