Restructured project

- backend moved to backend directory
- added and initialized frontend with vue
- moved infrastructure files to infra directory

backend/migrations/000006_create_positions.up.sql

@@ -0,0 +1,19 @@
+CREATE TABLE positions
+(
+    id             BIGSERIAL PRIMARY KEY,
+    receipt_id     BIGINT NOT NULL,
+    section_number TEXT,
+    gtin_code      TEXT,
+    product_name   TEXT    NOT NULL,
+    product_count  REAL    NOT NULL,
+    amount         REAL    NOT NULL,
+    discount       REAL,
+    surcharge      REAL,
+    tag            TEXT,
+    marking_code   TEXT,
+    ukz_code       TEXT,
+
+    FOREIGN KEY (receipt_id) REFERENCES receipts (id) ON DELETE CASCADE
+);
+
+CREATE INDEX idx_positions_receipt_id ON positions (receipt_id);