feat: Contexto Fiscal admin UI - reduces fiscal policy list to 3 real decisions

Adds an ADMIN-only "Contexto Fiscal" section to the Agent detail page: confirm/alter/clear the fiscal decisions
field_contract.resolve_product genuinely cannot derive from the ERP alone (icms_treatment, pis_cofins_profile,
entry_scope). Persists through the existing FiscalContextEntry table (the same one blocker_resolution already
writes operator answers into) - no new persistence model, no opaque JSON box. CSRF + RBAC + audit reuse the exact
mechanism already proven for /agents/{id}/features. Confirming or clearing flags every already-enriched product on
the installation for re-evaluation.

The list was reduced from 5 candidates to 3 by auditing real production data (Agent 2, 2026-09-27/28):
icms_rate/credit_rate and rounding were dropped - both proven NOT_APPLICABLE / ALREADY_DERIVED for this CRT=1
company from real field_contract dry-runs, not assumption. Real evidence surfaced in the UI is a dated, one-time
manual read-only measurement (disclosed in the card copy itself as such) - the Hub has no direct Firebird access,
so this is not a live query; a follow-up should pipe it through the heartbeat the same way CRT/CONTRIBUINTE_IPI
were wired.

Also found, during the same audit, that this client's NFC-e emission ignores the product's cadastral PIS/COFINS
CST/rate fields entirely (verified on the 3 real products that DO have them populated - the emitted documents never
carry the cadastral value) - documented as a strong OPEN recommendation for a future field_contract change, not
applied here, since changing canonical fiscal semantics needs accountant sign-off, not just my own inference.

1129 tests passed (tests + central/tests + agent/tests), 0 failed. Version 1.3.9 (single GTI_FISCAL_VERSION). Hub
only - Agent unchanged, no new installer this release.

tests/test_release_candidate.py

@@ -14,11 +14,11 @@ sys.path.insert(0, str(ROOT))
 def test_versions_are_coherent_across_hub_agent_and_packages():
     from central.app.version import GTI_FISCAL_VERSION
     v = (ROOT / "release" / "VERSION").read_text(encoding="utf-8").strip()
-    assert v == GTI_FISCAL_VERSION == "1.3.8"
+    assert v == GTI_FISCAL_VERSION == "1.3.9"
     pep = v.replace("-rc", "rc")
     for pp in ("central/pyproject.toml", "agent/pyproject.toml"):
         assert f'version = "{pep}"' in (ROOT / pp).read_text(encoding="utf-8")
-    assert '"AGENT_VERSION", "1.3.8"' in (ROOT / "agent" / "scripts" / "run_agent_service.py").read_text(encoding="utf-8")
+    assert '"AGENT_VERSION", "1.3.9"' in (ROOT / "agent" / "scripts" / "run_agent_service.py").read_text(encoding="utf-8")
     manifest = ROOT / "release" / "RELEASE_MANIFEST.json"
     if manifest.exists():
         m = json.loads(manifest.read_text(encoding="utf-8"))