fix: product_role never infers OWN_PRODUCTION from a single COMPOSICAO occurrence

Missão 4 / Bloco A.1 (prioridade máxima): central.app.field_contract.infer_role
treated ANY C000032.TIPO=COMPOSICAO row for a product as proof of own
production, with no ratio check - a beer sold 19 times and used once as a
recipe component (Agent 2, real data) was classified OWN_PRODUCTION from
that single occurrence, proposing to change its CFOP and IPPT.

New deterministic threshold in field_contract.py: COMPOSICAO must be a
majority (>=70%) of that product's own C000032 movement history, with at
least 5 total events, to count as own-production evidence. Below 30% the
evidence is discarded entirely (falls through to other role evidence,
e.g. TIPO=VENDA -> RESALE). Between 30% and 70% (with enough events to be
meaningful) is genuinely conflicting evidence -> UNKNOWN, never guessed
either way. RECEITA_INGREDIENTES/PROD_COZINHA-based evidence (a direct
recipe-table linkage, not a statistical ratio) is untouched.

agent/src/gti_fiscal_agent/firebird_reader.py now counts COMPOSICAO vs other
C000032 rows per product (read_product_evidence: single indexed query;
read_evidence: one grouped query for the whole catalog) into a new
ev["composed_ratio"] key, alongside the existing "composed" set (kept for
other, non-role consumers like coverage.py). central/app/enrichment/api.py's
sanitize_product_evidence and fiscal_completion.py's empty-ev fallback both
carry the new key through.

New tests (central/tests/test_field_contract.py) cover the 5 real cases named
in the mission: the beer (1 vs 19, 5% - discarded), a second beer (3 vs 4,
42.9% - MIXED/UNKNOWN), the liqueur (34 vs 22, 60.7% - still MIXED/UNKNOWN,
below the 70% bar), the juice with PROD_COZINHA=1+RECEITA_INGREDIENTES
(unaffected, stays OWN_PRODUCTION), and the tilapia/corvina fish (no
composed evidence at all, stays RESALE) - plus a strong 90% majority case
and an insufficient-sample (<5 events) case. A new end-to-end test in
agent/tests/test_cfop_ippt_auto_apply.py (committed separately, see the
feature/cfop-ippt-write branch) proves the weak-evidence beer never reaches
select_candidates as a write candidate, independent of any write flag.

Re-running the dry-run over Agent 2's real database (GTI.FDB, 527 products)
after this fix: AUTO_FILL_SAFE CFOP/IPPT cells drop from 12 to 3 (the two
fish CFOP fills + the juice's IPPT, all with strong, non-statistical
evidence) - docs/runs/GTI_dryrun_universe_summary_after_A1.json. This
corrects the Missão 3 report's 12/9(downgraded)/4(sustained) manual
judgment call with a deterministic, tested engine rule.

No schema/migration change. Zero Firebird writes (read-only analysis only).

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

central/app/enrichment/fiscal_completion.py

@@ -110,7 +110,7 @@ def resolve_fiscal_fields(session, *, product_code: str, description: str, curre
     refs = build_refs(session, uf=company.get("uf"), cfop_candidates=cfop_candidates)
     # Agent-provided, product_code-targeted evidence (recipes/composed/purchases/stock - see firebird_reader.read_product_evidence): a real,
     # indexed per-product query, never a full-table scan or a guess. Falls back to "no evidence" only when the Agent hasn't sent it yet.
-    ev = ev if isinstance(ev, dict) else {"recipes": set(), "composed": set(), "purchases": {}, "stock_entry": {}, "stock_in": {}}
+    ev = ev if isinstance(ev, dict) else {"recipes": set(), "composed": set(), "composed_ratio": {}, "purchases": {}, "stock_entry": {}, "stock_in": {}}
     d = decision or {"status": "EXACT_NCM", "cest_status": "NO_CEST_MAPPING_FOUND", "ba_st_mva_status": None, "classification": {"cest_candidates": [], "ipi_candidates": [], "ba_st_mva": {}}}
     raw = fc.resolve_product(p, d, company, refs, ev, ctx)
     out = {}