MIL-003: Step 2 - New flash cards

Review record RC-025 (Go, autonomous mode, not independent).

Task: MIL-003#1
Task: MIL-003#2
Task: MIL-003#3
Task: MIL-003#4
Task: MIL-003#5

src/flash_card/application/dto/card_dto.py

@@ -0,0 +1,21 @@
+"""Card data for the presentation layer.
+
+@file card_dto.py
+@brief The CardDto: a card as plain text.
+"""
+
+from dataclasses import dataclass
+
+
+@dataclass(frozen=True, slots=True)
+class CardDto:
+    """A card as plain data."""
+
+    ## @brief Word on the card front.
+    front_text: str
+    ## @brief Translation on the card back.
+    back_text: str
+    ## @brief Language code of the front.
+    front_language: str
+    ## @brief Language code of the back.
+    back_language: str