refactor(cleanup): remove dead ContactFolderPermission model file

Phase 2 cleanup: contact_folder_permission.py model was removed from
models/__init__.py and is no longer imported anywhere. The service,
schema, and routes remain as they delegate to EntityPermission.

Deleted:
- app/models/contact_folder_permission.py (dead model class)

Kept (still actively used):
- app/services/contact_folder_permission_service.py (delegates to EntityPermission)
- app/schemas/contact_folder_permission.py (pure Pydantic schemas)
- app/routes/contact_folder_permissions.py (registered in main.py)

app/models/contact_folder_permission.py

@@ -1,90 +0,0 @@
-"""Contact folder permission model — ACLs for folder sharing."""
-
-from __future__ import annotations
-
-import uuid
-from datetime import datetime
-
-from sqlalchemy import (
-    Boolean,
-    CheckConstraint,
- DateTime,
-    ForeignKey,
-    Index,
-    String,
-    UniqueConstraint,
-    func,
-)
-from sqlalchemy.dialects.postgresql import UUID as PGUUID
-from sqlalchemy.orm import Mapped, mapped_column
-
-from app.core.db import Base, TenantMixin
-
-
-class ContactFolderPermission(Base, TenantMixin):
-    """ACL entry for a contact folder.
-
-    Grants a specific permission level to a user or group for a folder.
-    When ``inherit_to_subfolders`` is True, the permission also applies
-    to all descendant folders.
-
-    Permission levels:
-    - ``none``   — no access (explicit deny)
-    - ``read``   — view folder and its contacts
-    - ``write``  — read + edit contacts, add contacts to folder
-    - ``admin``  — read + write + delete contacts + manage folder permissions
-    """
-
-    __tablename__ = "contact_folder_permissions"
-    __table_args__ = (
-        UniqueConstraint(
-            "folder_id",
-            "user_id",
-            "group_id",
-            "tenant_id",
-            name="uq_cfp_folder_user_group_tenant",
-        ),
-        # Ensure exactly one of user_id or group_id is set (not both, not neither)
-        CheckConstraint(
-            "(user_id IS NOT NULL AND group_id IS NULL) OR "
-            "(user_id IS NULL AND group_id IS NOT NULL)",
-            name="ck_cfp_exactly_one_principal",
-        ),
-        Index("ix_cfp_folder", "folder_id"),
-        Index("ix_cfp_user", "user_id"),
-        Index("ix_cfp_group", "group_id"),
-        Index("ix_cfp_tenant", "tenant_id"),
-    )
-
-    id: Mapped[uuid.UUID] = mapped_column(
-        PGUUID(as_uuid=True), primary_key=True, default=uuid.uuid4
-    )
-    folder_id: Mapped[uuid.UUID] = mapped_column(
-        PGUUID(as_uuid=True),
-        ForeignKey("contact_folders.id", ondelete="CASCADE"),
-        nullable=False,
-        index=True,
-    )
-    user_id: Mapped[uuid.UUID | None] = mapped_column(
-        PGUUID(as_uuid=True),
-        ForeignKey("users.id", ondelete="CASCADE"),
-        nullable=True,
-    )
-    group_id: Mapped[uuid.UUID | None] = mapped_column(
-        PGUUID(as_uuid=True),
-        ForeignKey("groups.id", ondelete="CASCADE"),
-        nullable=True,
-    )
-    permission_level: Mapped[str] = mapped_column(
-        String(20), nullable=False, default="read"
-    )  # none | read | write | admin
-    inherit_to_subfolders: Mapped[bool] = mapped_column(
-        Boolean, nullable=False, default=True, server_default="true"
-    )
-    created_at: Mapped[datetime] = mapped_column(
-        DateTime(timezone=True), nullable=False, server_default=func.now()
-    )
-    updated_at: Mapped[datetime] = mapped_column(
-        DateTime(timezone=True), nullable=False, server_default=func.now(),
-        onupdate=func.now(),
-    )