feat(v2): real Slack send pipeline (guard, idempotency, success/failure registration)

Implements the actual send branch: Selecionar Top N -> Montar Mensagem ->
Guard de Envio -> Slack real -> registrar resultado (only after
confirmed success/failure) -- previously simulated/absent.

logic/slack.js (new): shouldSendByConfig (SEND_ENABLED gate, defaults
false), computeMessageHash (djb2Hash of the exact message text, reused
from logic/hash.js), alreadySentSuccessfully (idempotency check: only a
prior status='success' record for the same report_date+run_type+
message_hash blocks a resend -- a prior 'failed' record does not, so
retries after a real failure aren't stuck), evaluateSendGuard (single
auditable decision combining both), buildEnvioDigestRecord.
logic/slack.test.js: 13 tests covering all of the above, explicitly
labeled against the mission's required tests #13-#16.

New node drivers:
- guard-envio-slack.node.js: reads the digest + recent envio records
  (fetched by report_date), computes the send decision.
- Slack node itself (n8n-nodes-base.slack, native, not a raw webhook):
  reuses the real "Slack account" credential (slackApi) and
  $vars.SLACK_CHANNEL_TECNICO channel variable already used by this
  org's own "Notificacao de Erros Globais" workflow on the same n8n
  instance -- V1's own Slack webhook URL was never actually deployed
  (its Config value is literally "SEU/WEBHOOK/AQUI", same class of
  placeholder as the old GLPI URL from the prior cycle), so this reuses
  the one REAL, credentialed Slack mechanism that exists in this
  environment rather than inventing a new destination. onError:
  continueErrorOutput splits success/failure into two branches.
- registrar-envio-sucesso.node.js / registrar-envio-falha.node.js: build
  the success/failure record; only the success path continues to the
  existing per-ticket send-counter logic (rewired below).
- lancar-erro-envio.node.js: after the failure record is written,
  explicitly throws so the n8n execution shows status=error (never
  silently swallow a send failure).
- pular-envio.node.js: terminal no-op for the "should not send" branch
  (SEND_ENABLED=false or already sent today), for observability only.

n8n/nodes/prepare-envio-record.node.js: rewired to read the Top10
selection by name ($('Code - Selecionar Top 10').all()) instead of
$input, since it now runs downstream of the Slack-success registration,
not directly off Selecionar Top10 -- registering per-ticket send counts
before Slack ever confirmed anything was the exact "don't register
before confirmation" bug the mission called out.

logic/message.test.js: added a full-Top10 message-length regression test
(mission requirement: message stays short, no leaked JSON/score/evidence).

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

n8n/nodes/prepare-envio-record.node.js

@@ -1,6 +1,9 @@
 const ONE_DAY = 24 * 60 * 60 * 1000;
 
-return $input.all()
+// So roda depois de "Data Table - Registrar Envio Digest (Sucesso)" -- ou seja, so depois do
+// Slack confirmar sucesso de verdade (missao "finalizacao para producao", secao 19). Os dados
+// do Top10 sao lidos por nome (nao por $input, que aqui e o registro do envio, nao os tickets).
+return $('Code - Selecionar Top 10').all()
   .filter((item) => item.json._grupo === 'selected')
   .map((item) => {
     const data = item.json;