chore: restructure project into backend and frontend folders

- Move all frontend code to frontend/ directory
- Add backend/ with Go project structure (cmd, internal, pkg)
- Add docker-compose.yml for orchestration

backend/internal/db/queries/query.sql

@@ -0,0 +1,16 @@
+-- name: GetDeliveriesByDate :many
+SELECT * FROM deliveries WHERE date = $1;
+ 
+-- name: CreateDelivery :one
+INSERT INTO deliveries (date, pickup_location, product_name, address, phone, additional_phone, has_elevator, comment)
+VALUES ($1, $2, $3, $4, $5, $6, $7, $8)
+RETURNING *;
+
+-- name: GetDeliveryByID :one
+SELECT * FROM deliveries WHERE id = $1;
+
+-- name: DeleteDelivery :exec
+DELETE FROM deliveries WHERE id = $1;
+
+-- name: UpdateDelivery :exec
+UPDATE deliveries SET date = $1, pickup_location = $2, product_name = $3, address = $4, phone = $5, additional_phone = $6, has_elevator = $7, comment = $8, updated_at = NOW() WHERE id = $9;