deployment: rename DATA_DIR/CHECKOUT_DATA_DIR to CART_DIR/CHECKOUT_DIR

The binaries read CART_DIR (cmd/cart) and CHECKOUT_DIR (cmd/checkout,
cmd/backoffice); the deployment set DATA_DIR/CHECKOUT_DATA_DIR which
nothing reads, so storage fell back to the ephemeral relative ./data and
was wiped on every redeploy. Use the names the code actually reads.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

deployment/deployment.yaml

@@ -76,9 +76,9 @@ spec:
               memory: "70Mi"
               cpu: "1200m"
           env:
-            - name: DATA_DIR
+            - name: CART_DIR
               value: "/data/cart-actor"
-            - name: CHECKOUT_DATA_DIR
+            - name: CHECKOUT_DIR
               value: "/data/checkout-actor"
             - name: TZ
               value: "Europe/Stockholm"
@@ -184,9 +184,9 @@ spec:
               memory: "70Mi"
               cpu: "1200m"
           env:
-            - name: DATA_DIR
+            - name: CART_DIR
               value: "/data/cart-actor"
-            - name: CHECKOUT_DATA_DIR
+            - name: CHECKOUT_DIR
               value: "/data/checkout-actor"
             - name: TZ
               value: "Europe/Stockholm"