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>

n8n/nodes/build-sql-candidatos.node.test.js

@@ -17,3 +17,8 @@ test('SQL de candidatos V2 NAO tem mais LIMIT fixo em 10 (funil maior)', () => {
   assert.ok(sql.includes('LIMIT {CANDIDATE_POOL_SIZE}'));
   assert.ok(!sql.includes('LIMIT 10'));
 });
+
+test('SQL de candidatos V2 traz a descricao real do chamado (t.content) para a IA', () => {
+  const sql = fs.readFileSync(path.join(__dirname, '..', '..', 'sql', 'candidatos_v2_glpi.sql'), 'utf8');
+  assert.ok(sql.includes('t.content AS descricao'));
+});