fix: close five final-review gaps in all-categories mode

- .detect_direct_suppressed() keys on (year, canonical_govid, category);
  all-categories mode collapses category to one literal value, so the key
  collides and the detector silently reports FALSE instead of "unknown".
  Report NA there instead, and stop isTRUE() in .build_provenance() from
  collapsing that NA back to FALSE. Schema widened to allow null.
- Refuse complete = TRUE + category = "All Categories": the completion grid
  has no per-category cells left to fill once categories are collapsed,
  so the prior silent 0-rows-filled result was never actually checked.
- cog_balances(category = "All Categories") returned zero rows with no
  error. .validate_verb_inputs() gains allow_all_categories (default
  FALSE); .verb_spendrev() passes TRUE, cog_balances() does not, so the
  three verbs share one place to reject it instead of drifting again.
- Fix the false `subtype = "operations"` argument claim (no such argument
  exists) in NEWS.md and an internal spending.R comment.

Adds three covering tests to test-all-categories.R for the three
behaviour changes above.

inst/schemas/provenance-v1.json

@@ -22,8 +22,8 @@
       "description": "How the intergovernmental leg was assembled; null for 'primary' and 'direct'."
     },
     "expenditure_concept_direct_suppressed": {
-      "type": "boolean",
-      "description": "TRUE when expenditure_concept = 'total' and at least one requested (year, category) has intergovernmental rows but NO Direct rows in this corpus (typically a legacy aggregate-only family) -- those result rows report the intergovernmental leg alone, not Direct + IG. Always FALSE for expenditure_concept = 'primary' or 'direct'. See the affected rows' `notes` for the recovering recipe, if any."
+      "type": ["boolean", "null"],
+      "description": "TRUE when expenditure_concept = 'total' and at least one requested (year, category) has intergovernmental rows but NO Direct rows in this corpus (typically a legacy aggregate-only family) -- those result rows report the intergovernmental leg alone, not Direct + IG. Always FALSE for expenditure_concept = 'primary' or 'direct'. null (NA) when expenditure_concept = 'total' AND category = 'All Categories': the detector keys on per-category rows, which that mode collapses, so suppression cannot be computed -- see `expenditure_concept_note`. See the affected rows' `notes` for the recovering recipe, if any."
     },
     "revenue_concept": {
       "type": "string",