refactor: add proper types for all database insert operations

- Add missing Select and Insert types for Auth.js tables (Account, Session, VerificationToken)
- Update all insert operations to use typed New* variables:
  - NewUser for user signup
  - NewItem for adding wishlist items
  - NewSavedWishlist for saving wishlists
- Improves type safety and catches insert errors at compile time

src/lib/db/schema.ts

@@ -177,6 +177,12 @@ export const usersRelations = relations(users, ({ many }) => ({
 
 export type User = typeof users.$inferSelect;
 export type NewUser = typeof users.$inferInsert;
+export type Account = typeof accounts.$inferSelect;
+export type NewAccount = typeof accounts.$inferInsert;
+export type Session = typeof sessions.$inferSelect;
+export type NewSession = typeof sessions.$inferInsert;
+export type VerificationToken = typeof verificationTokens.$inferSelect;
+export type NewVerificationToken = typeof verificationTokens.$inferInsert;
 export type Wishlist = typeof wishlists.$inferSelect;
 export type NewWishlist = typeof wishlists.$inferInsert;
 export type Item = typeof items.$inferSelect;