chore(deploy): add database maintenance and migration options

Added new deployment options to deploy.sh:
- --migrate: Runs Prisma migration deploy command
- --clean-database: Executes maintenance SQL to clean data while preserving categories

Added new maintenance directory backend/prisma/maintenance/ containing:
- clean-database.sql: SQL script for database cleaning operations

Updated deployment script to:
- Include new command-line flags in help text
- Add conditional blocks for running migrations and database cleaning
- Implement container readiness checks before running Prisma commands
- Preserve existing seed functionality while adding new maintenance features

backend/prisma/maintenance/clean-database.sql

@@ -0,0 +1,24 @@
+-- Rensar applikationsdata men behaller kategorier.
+-- Uppdatera den har filen nar nya tabeller tillkommer i schema.prisma.
+
+SET FOREIGN_KEY_CHECKS = 0;
+
+DELETE FROM `FlyerSelection`;
+DELETE FROM `FlyerItem`;
+DELETE FROM `FlyerSession`;
+
+DELETE FROM `ShoppingListItem`;
+DELETE FROM `ShoppingList`;
+
+DELETE FROM `InventoryTransaction`;
+DELETE FROM `InventoryItem`;
+
+DELETE FROM `RecipeIngredient`;
+DELETE FROM `Recipe`;
+
+DELETE FROM `PantryItem`;
+DELETE FROM `MealPlanItem`;
+
+DELETE FROM `Product`;
+
+SET FOREIGN_KEY_CHECKS = 1;