Add user dashboard and per-user food item ownership

Introduces a user dashboard route and template, moving dashboard logic to a user blueprint. FoodItem now has an owner_id field and a unique constraint on (barcode, owner_id), with relationships set up in the User model. Updates food item creation to associate with the current user, and adds a utility script for dropping a temporary table.

temp.py

@@ -0,0 +1,15 @@
+from application import db, app
+from sqlalchemy import MetaData, Table
+
+with app.app_context():
+    table_name = "_alembic_tmp_food_item"
+    engine = db.engine
+    metadata = MetaData()
+    metadata.reflect(bind=engine)
+
+    if table_name in metadata.tables:
+        tmp_table = Table(table_name, metadata, autoload_with=engine)
+        tmp_table.drop(engine)
+        print(f"Table '{table_name}' dropped.")
+    else:
+        print(f"No table named '{table_name}' found.")