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/alembic/versions/0032_contribuinte_ipi.py

@@ -0,0 +1,21 @@
+"""Installation.company_contribuinte_ipi: auto-discovered (C000004.CONTRIBUINTE_IPI, same row/query as company_crt) at heartbeat, never
+operator-guessed. Closes the fiscal-completion gap where CST_IPI could not be resolved without asking a human for a fact the ERP already proves.
+
+Revision ID: 0032_contribuinte_ipi
+Revises: 0031_enrichment_reevaluate
+"""
+from alembic import op
+import sqlalchemy as sa
+
+revision = "0032_contribuinte_ipi"
+down_revision = "0031_enrichment_reevaluate"
+branch_labels = None
+depends_on = None
+
+
+def upgrade():
+    op.add_column("installations", sa.Column("company_contribuinte_ipi", sa.String(1), nullable=True))
+
+
+def downgrade():
+    op.drop_column("installations", "company_contribuinte_ipi")