Sheet naming — let users name uploads at generation time

[emares17]

Problem

All sheets in the Inventory history are identified only by their original CSV/Excel filename. Users have no way to give a meaningful name to a batch (e.g. "Warehouse A - April restock").

Solution

• Add an optional text input on the upload page above the Generate button
• Store the value in a new sheet_name column on the user_sheets table (falls back to original_filename when blank)
• Display sheet_name in the Inventory Sheet History table instead of original_filename
• Old sheets without a name continue to show original_filename as before

Schema change

ALTER TABLE user_sheets ADD COLUMN sheet_name text;