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/fallback.js

@@ -1,11 +1,18 @@
+// AI_FALLBACK e um estado tecnico: significa "a IA nunca analisou este chamado" (erro,
+// timeout, IA desligada, JSON invalido, ou cortado pelo limite de AI_MAX_CANDIDATES). NAO e
+// uma conclusao da IA -- por isso nunca usa uma das 11 classes que a IA pode retornar
+// (ver logic/classification.js). Politica de elegibilidade fica centralizada em
+// logic/cooldown.js (applyFallbackPolicy), nao aqui.
+const AI_FALLBACK_CLASSIFICATION = 'AI_FALLBACK';
+
 function buildFallbackClassification(reason) {
   return {
-    classification: 'ACTIONABLE_NOW',
-    actionable_today: true,
+    classification: AI_FALLBACK_CLASSIFICATION,
+    actionable_today: false,
     confidence: 0,
     blocker_type: null,
     waiting_for: null,
-    next_action: 'Revisar chamado manualmente',
+    next_action: 'Revisar chamado manualmente (nao analisado pela IA)',
     suggested_action_type: 'manual_review',
     business_risk: 'medium',
     reason: `Fallback deterministico: ${reason}`,
@@ -15,4 +22,4 @@ function buildFallbackClassification(reason) {
   };
 }
 
-module.exports = { buildFallbackClassification };
+module.exports = { buildFallbackClassification, AI_FALLBACK_CLASSIFICATION };