feat: wire field_contract into product enrichment; auto-discover CRT/CONTRIBUINTE_IPI at heartbeat; targeted per-product ERP evidence

field_contract.resolve_product was only exercised by its own unit tests. /v1/products/resolve now calls it for every product whose NCM
resolves, merging CFOP/CST/CSOSN/PIS-COFINS/CST_IPI/SITUACAO_TRIBUTARIA/IAT/IPPT decisions alongside CLASSIFICACAO_FISCAL/CEST/IPI - reusing
the same engine, the same FiscalContextEntry table the blocker-resolution workflow already writes to, no duplicated rules.

Closes three real transport/discovery gaps found while wiring it in:
- Agent heartbeat never sent company_crt (env-var UF only) or company_contribuinte_ipi, so Installation.company_crt stayed permanently empty
  even though company_context.resolve() already proves both from C000004/EMISSOR for every coverage job. Resolved once, cached, retried only
  while unresolved. Migration 0032 adds Installation.company_contribuinte_ipi (NULL=unknown, never coerced to "N").
- The Agent's enrichment payload only ever reported 3 old fields (CLASSIFICACAO_FISCAL/CEST/IPI) as "current", so the Hub could never see the
  product's own CFOP/CST/CSOSN/... nor the classification columns (TIPO/PROD_COZINHA/PRODUTO_SERVICO/CODGRUPO) infer_role needs - separated
  into a read-only CURRENT_REPORT_FIELDS list, the write allowlist (PRODUCT_ENRICHMENT_WRITE_V1) untouched.
- Added a targeted, product_code-scoped evidence query (firebird_reader.read_product_evidence: recipes/composed/purchases/stock, indexed WHERE,
  never a full-table scan) so st_withheld/product_role can be proven for a single ad-hoc resolve, not only during a full sync job.

Verified read-only against the real database (D:\PROJETOS\GTISISTEMAS\Banco\GTI.FDB): CRT=1, CONTRIBUINTE_IPI=N, company_context.resolve()
reaches HIGH confidence; infer_role correctly resolved RESALE/OWN_PRODUCTION for 5/8 sample real products with zero operator questions.

1121 tests passed (tests + central/tests + agent/tests), 0 failed. Version 1.3.7 (single GTI_FISCAL_VERSION shared by Hub and Agent per
central/app/version.py's own design - never independently versioned).

central/app/api.py

@@ -184,7 +184,7 @@ def router(session_factory, bootstrap_token):
                 installation = Installation(agent_id=agent.id, tenant_id=agent.tenant_id, installation_id=installation_key, display_name=supplied.get("display_name") or agent.name,
                                             features_configured=True, corrector_enabled=True)      # legacy/bootstrap self-registration keeps the pre-existing behaviour
                 session.add(installation); session.flush()
-            fields = {"display_name": supplied.get("display_name"), "customer_code": supplied.get("customer_code"), "notes": supplied.get("notes"), "hostname": supplied.get("hostname"), "windows_version": supplied.get("windows_version"), "machine_fingerprint": supplied.get("machine_fingerprint"), "company_code": supplied.get("company_code"), "company_name": supplied.get("company_name"), "company_cnpj_masked": supplied.get("company_cnpj_masked"), "company_uf": supplied.get("company_uf"), "company_crt": supplied.get("company_crt"), "firebird_version": supplied.get("firebird_version"), "firebird_ods": supplied.get("firebird_ods"), "database_identifier": supplied.get("database_identifier"), "capabilities": supplied.get("capabilities"), "fiscal_engine_version": supplied.get("fiscal_engine_version"), "dataset_versions": supplied.get("dataset_versions"), "last_status": supplied.get("status") or payload.get("status"), "last_seen_at": now}
+            fields = {"display_name": supplied.get("display_name"), "customer_code": supplied.get("customer_code"), "notes": supplied.get("notes"), "hostname": supplied.get("hostname"), "windows_version": supplied.get("windows_version"), "machine_fingerprint": supplied.get("machine_fingerprint"), "company_code": supplied.get("company_code"), "company_name": supplied.get("company_name"), "company_cnpj_masked": supplied.get("company_cnpj_masked"), "company_uf": supplied.get("company_uf"), "company_crt": supplied.get("company_crt"), "company_contribuinte_ipi": supplied.get("company_contribuinte_ipi"), "firebird_version": supplied.get("firebird_version"), "firebird_ods": supplied.get("firebird_ods"), "database_identifier": supplied.get("database_identifier"), "capabilities": supplied.get("capabilities"), "fiscal_engine_version": supplied.get("fiscal_engine_version"), "dataset_versions": supplied.get("dataset_versions"), "last_status": supplied.get("status") or payload.get("status"), "last_seen_at": now}
             for key, value in fields.items():
                 if value is not None: setattr(installation, key, value)
             if supplied.get("started_at"):