feat(crm): dominio backend (cuentas, contactos, prospectos, embudos, oportunidades, actividades)

- Nuevo schema `crm` con 7 tablas multi-tenant (TenantScopedMixin + soft delete)
- Módulos FastAPI por dominio: models/dto/service/routes (patrón example)
- Métricas del dashboard (KPIs + embudo por etapa)
- Conversión de prospecto → cuenta/contacto/oportunidad (idempotente)
- Movimiento de oportunidad entre etapas (Kanban) con estado/probabilidad derivados
- 25 permisos registrados en PermissionRegistry
- Migración Alembic con upgrade/downgrade completos
- 24 tests de servicios (pytest) en verde

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

backend/api/v1/modules/crm/activities/dto.py

@@ -0,0 +1,51 @@
+from datetime import datetime
+
+from pydantic import BaseModel, ConfigDict, Field
+
+
+class ActivityCreate(BaseModel):
+    activity_type: str = Field(..., max_length=20)
+    subject: str = Field(..., min_length=1, max_length=255)
+    description: str | None = None
+    status: str = Field("pending", max_length=20)
+    due_date: datetime | None = None
+    account_id: int | None = None
+    contact_id: int | None = None
+    lead_id: int | None = None
+    opportunity_id: int | None = None
+    owner_user_id: str | None = Field(None, max_length=64)
+
+
+class ActivityUpdate(BaseModel):
+    activity_type: str | None = Field(None, max_length=20)
+    subject: str | None = Field(None, min_length=1, max_length=255)
+    description: str | None = None
+    status: str | None = Field(None, max_length=20)
+    due_date: datetime | None = None
+    completed_at: datetime | None = None
+    account_id: int | None = None
+    contact_id: int | None = None
+    lead_id: int | None = None
+    opportunity_id: int | None = None
+    owner_user_id: str | None = Field(None, max_length=64)
+
+
+class ActivityResponse(BaseModel):
+    model_config = ConfigDict(from_attributes=True)
+
+    id: int
+    activity_type: str
+    subject: str
+    description: str | None
+    status: str
+    due_date: datetime | None
+    completed_at: datetime | None
+    account_id: int | None
+    contact_id: int | None
+    lead_id: int | None
+    opportunity_id: int | None
+    owner_user_id: str | None
+    tenant_id: int
+    company_id: int
+    created_at: datetime
+    updated_at: datetime