test(0035e): cobertura del visual heredado, threshold override y migracion idempotente

- test_group_visual_inheritance.py (4 tests): homogeneo->Url heredado,
  heterogeneo->generico Group, vacio->generico, subgrupos anidados
  ignorados.
- test_manifest_threshold_override.py (4 tests): override 100 con 80
  unicas no agrupa; override bajo (20) si agrupa cuando se supera;
  threshold=0 cae al default 50; mirror Python del parser de manifest
  C++ confirma el campo se extrae como int.
- test_schema_migration_group_id.py (3 tests): mirror Python de
  project_migrate_schema, verifica idempotencia (1a y 2a apertura
  no duplican columna), no-op sobre BD ya migrada, datos previos
  sobreviven la migracion.

tests/test_group_visual_inheritance.py

@@ -0,0 +1,121 @@
+"""Tests del visual heredado del Group (issue 0035e).
+
+El binario C++ implementa `apply_group_inherited_visuals` en data.cpp:
+para cada nodo Group del grafo, consulta `SELECT DISTINCT type_ref
+FROM entities WHERE group_id = ? AND type_ref != 'Group'`. Si la
+familia es homogenea (un solo tipo), reasigna el `type_id` del nodo
+Group al de ese tipo y fija `shape_override = SHAPE_SQUARE`. Si es
+heterogenea o vacia, conserva el visual generico.
+
+El subcomando `gx-cli group visual <id>` espejea exactamente esa SQL,
+asi estos tests verifican el contrato (homogeneo vs heterogeneo,
+type heredado y shape=square preservado) sin depender del binario.
+"""
+from __future__ import annotations
+
+import sqlite3
+
+from test_gx_cli import OPS_SCHEMA, APP_SCHEMA, env_dirs, run_gx  # noqa: F401
+
+
+def _seed_group_with_children(ops_db, group_id: str,
+                                child_specs: list[tuple[str, str]]):
+    """Inserta el contenedor Group + cada hijo (id, type_ref).
+
+    `child_specs` = [(child_id, type_ref), ...]. Se anaden con group_id
+    apuntando al contenedor.
+    """
+    cn = sqlite3.connect(ops_db)
+    try:
+        cn.execute(
+            "INSERT INTO entities(id, name, type_ref, status, source, "
+            "                     metadata, created_at, updated_at) "
+            "VALUES (?, ?, 'Group', 'active', 'manual', '{}', "
+            "        '2026-05-04T10:00:00.000Z', '2026-05-04T10:00:00.000Z')",
+            (group_id, "test-group"),
+        )
+        for i, (cid, type_ref) in enumerate(child_specs):
+            cn.execute(
+                "INSERT INTO entities(id, name, type_ref, status, source, "
+                "                     metadata, group_id, "
+                "                     created_at, updated_at) "
+                "VALUES (?, ?, ?, 'active', 'manual', '{}', ?, ?, ?)",
+                (cid, f"name-{i}", type_ref, group_id,
+                 f"2026-05-04T11:{i:02d}:00.000Z",
+                 f"2026-05-04T11:{i:02d}:00.000Z"),
+            )
+        cn.commit()
+    finally:
+        cn.close()
+
+
+def test_group_inherits_visual_from_homogeneous_children(env_dirs):
+    """5 Urls como hijos -> visual heredado a 'Url' (homogeneo)."""
+    children = [(f"u_{i:02d}", "Url") for i in range(5)]
+    _seed_group_with_children(env_dirs["ops"], "G_homogeneous", children)
+    out = run_gx(env_dirs, "group", "visual", "G_homogeneous")
+    assert out["homogeneous"] is True, out
+    assert out["inherited"] == "Url", out
+    assert out["child_types"] == ["Url"], out
+    # La forma siempre se queda como square — distintivo de contenedor.
+    assert out["shape"] == "square", out
+
+
+def test_group_falls_back_to_generic_for_heterogeneous(env_dirs):
+    """Url + Email en el mismo Group -> visual generico Group."""
+    children = [
+        ("u_00", "Url"),    ("u_01", "Url"),    ("u_02", "Url"),
+        ("e_00", "Email"),  ("e_01", "Email"),
+    ]
+    _seed_group_with_children(env_dirs["ops"], "G_heterogeneous", children)
+    out = run_gx(env_dirs, "group", "visual", "G_heterogeneous")
+    assert out["homogeneous"] is False, out
+    assert out["inherited"] == "Group", out
+    # child_types ordenado alfabeticamente — verifica ambos presentes.
+    assert out["child_types"] == ["Email", "Url"], out
+    assert out["shape"] == "square", out
+
+
+def test_group_with_no_children_falls_back_to_generic(env_dirs):
+    """Group vacio (sin hijos con group_id apuntando a el) -> generico."""
+    _seed_group_with_children(env_dirs["ops"], "G_empty", [])
+    out = run_gx(env_dirs, "group", "visual", "G_empty")
+    assert out["homogeneous"] is False, out
+    assert out["inherited"] == "Group", out
+    assert out["child_types"] == [], out
+
+
+def test_group_visual_ignores_nested_subgroups(env_dirs):
+    """Subgrupos anidados (type_ref='Group') no cuentan — siguen scope fase 1."""
+    cn = sqlite3.connect(env_dirs["ops"])
+    try:
+        cn.execute(
+            "INSERT INTO entities(id, name, type_ref, status, source, "
+            "                     metadata, created_at, updated_at) "
+            "VALUES ('G_outer', 'outer', 'Group', 'active', 'manual', '{}', "
+            "        '2026-05-04T10:00:00.000Z', '2026-05-04T10:00:00.000Z')"
+        )
+        for i in range(3):
+            cn.execute(
+                "INSERT INTO entities(id, name, type_ref, status, source, "
+                "                     metadata, group_id, "
+                "                     created_at, updated_at) "
+                "VALUES (?, ?, 'Url', 'active', 'manual', '{}', 'G_outer', "
+                "        '2026-05-04T11:00:00.000Z', '2026-05-04T11:00:00.000Z')",
+                (f"u_{i}", f"url-{i}"),
+            )
+        # Subgrupo anidado — el resolver lo excluye via type_ref != 'Group'.
+        cn.execute(
+            "INSERT INTO entities(id, name, type_ref, status, source, "
+            "                     metadata, group_id, "
+            "                     created_at, updated_at) "
+            "VALUES ('G_nested', 'nested', 'Group', 'active', 'manual', "
+            "        '{}', 'G_outer', "
+            "        '2026-05-04T11:00:00.000Z', '2026-05-04T11:00:00.000Z')"
+        )
+        cn.commit()
+    finally:
+        cn.close()
+    out = run_gx(env_dirs, "group", "visual", "G_outer")
+    assert out["homogeneous"] is True, out
+    assert out["inherited"] == "Url", out