Merge prod_v5 (catalog v2.7, warehouse locking, per-project accept) into integration

Conflict in init_db.py resolved keeping the audit_log table ensure
function (new-one) — prod_v5 predates it and its side was empty.
Both sides' SQL lands: audit_log table plus the category-free materials
model.

backend/app/models/catalog.py

@@ -130,14 +130,11 @@ class CategoryAttribute(Base):
 
 class Material(Base):
     __tablename__ = "materials"
-    # v2.5/2.6: name is GLOBALLY unique; category_id is nullable + derived.
+    # v2.6/v2.7: name is GLOBALLY unique; decoupled from categories.
     __table_args__ = (UniqueConstraint("name", name="uq_material_name"),)
     __mapper_args__ = {"eager_defaults": True}
 
     id: Mapped[uuid.UUID] = _uuid_pk()
-    category_id: Mapped[uuid.UUID | None] = mapped_column(
-        ForeignKey("material_categories.id", ondelete="RESTRICT")
-    )
     name: Mapped[str] = mapped_column(Text, nullable=False)
     topic: Mapped[str | None] = mapped_column(Text)  # تاپیک جلوی برنامه (Persian) — legacy
     canonical_unit_id: Mapped[int] = mapped_column(
@@ -149,7 +146,6 @@ class Material(Base):
         DateTime(timezone=True), nullable=False, server_default=func.now(), onupdate=func.now()
     )
 
-    category: Mapped["MaterialCategory | None"] = relationship(lazy="raise")
     canonical_unit: Mapped["Unit"] = relationship(lazy="raise")
     attribute_values: Mapped[list["MaterialAttributeValue"]] = relationship(
         back_populates="material", lazy="raise", passive_deletes=True