fixed remove issue, made items avaiable for available view

trade-hub/backend/app/models.py

@@ -74,6 +74,10 @@ class InventoryEntry(Base):
     __table_args__ = (
         UniqueConstraint("user_id", "class_name", name="uq_inventory_user_item"),
         CheckConstraint("quantity >= 1", name="ck_inventory_quantity_positive"),
+        CheckConstraint(
+            "visibility IN ('private', 'available')",
+            name="ck_inventory_visibility",
+        ),
     )
 
     id: Mapped[int] = mapped_column(Integer, primary_key=True, autoincrement=True)
@@ -83,6 +87,12 @@ class InventoryEntry(Base):
     class_name: Mapped[str] = mapped_column(String(255), nullable=False)
     quantity: Mapped[int] = mapped_column(Integer, nullable=False, default=1)
     notes: Mapped[str] = mapped_column(Text, nullable=False, default="")
+    # "private" (default): only the owner sees the row. "available": the owner
+    # is offering the item. Unrelated to the response flag `available`, which
+    # only reports whether the catalog still contains the referenced item.
+    visibility: Mapped[str] = mapped_column(
+        String(16), nullable=False, default="private", server_default="private"
+    )
     created_at: Mapped[datetime] = mapped_column(
         DateTime(timezone=True), nullable=False, default=utcnow
     )