fix(v2): AI_FALLBACK replaces the ACTIONABLE_NOW-with-confidence-0 lie, normalize null-like strings

Fallback (ai_disabled, ai_error, invalid_json, ai_max_candidates_cap --
any candidate the AI never actually analyzed) now produces classification
'AI_FALLBACK', an explicit technical state that is never part of the
11-class enum sent to OpenAI (the AI itself can never legitimately return
it). Previously it silently claimed ACTIONABLE_NOW with confidence 0,
which made unanalyzed tickets indistinguishable from genuinely confirmed
ones at the classification-label level.

Also normalizes blocker_type/waiting_for when the model returns the
literal string "null"/"none"/"n/a"/"" instead of JSON null -- done
once, in the validation layer (logic/classification.js), not scattered
around the workflow.

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

logic/classification.js

@@ -4,6 +4,18 @@ const VALID_CLASSIFICATIONS = [
   'PROJECT_LONG_TERM', 'DUPLICATE_OR_OBSOLETE', 'INSUFFICIENT_CONTEXT',
 ];
 
+// O modelo, apesar do schema permitir null de verdade em blocker_type/waiting_for, as vezes
+// devolve a STRING "null" (ou variantes equivalentes) em vez do valor JSON null. Normaliza
+// aqui, na camada de validacao -- unico lugar que toca a resposta crua da IA.
+const NULL_LIKE_STRINGS = new Set(['null', 'none', 'n/a', 'na', '']);
+
+function normalizeNullableString(value) {
+  if (value === null || value === undefined) return null;
+  const trimmed = String(value).trim();
+  if (NULL_LIKE_STRINGS.has(trimmed.toLowerCase())) return null;
+  return trimmed;
+}
+
 function validateAiClassification(raw) {
   const errors = [];
   if (!raw || typeof raw !== 'object') {
@@ -28,8 +40,8 @@ function validateAiClassification(raw) {
       classification: raw.classification,
       actionable_today: raw.actionable_today,
       confidence,
-      blocker_type: raw.blocker_type ?? null,
-      waiting_for: raw.waiting_for ?? null,
+      blocker_type: normalizeNullableString(raw.blocker_type),
+      waiting_for: normalizeNullableString(raw.waiting_for),
       next_action: raw.next_action,
       suggested_action_type: raw.suggested_action_type ?? 'technical_action',
       business_risk: raw.business_risk ?? 'medium',
@@ -41,4 +53,4 @@ function validateAiClassification(raw) {
   };
 }
 
-module.exports = { VALID_CLASSIFICATIONS, validateAiClassification };
+module.exports = { VALID_CLASSIFICATIONS, validateAiClassification, normalizeNullableString };