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/domain/entities/vocabulary.py

@@ -0,0 +1,20 @@
+"""The delivered word list.
+
+@file vocabulary.py
+@brief The Vocabulary entity: all cards of a language pair.
+"""
+
+from dataclasses import dataclass
+
+from flash_card.domain.entities.card import Card
+from flash_card.domain.value_objects.language_pair import LanguagePair
+
+
+@dataclass(frozen=True, slots=True)
+class Vocabulary:
+    """All cards of a language pair as delivered."""
+
+    ## @brief The languages of the cards.
+    language_pair: LanguagePair
+    ## @brief The cards in file order.
+    cards: tuple[Card, ...]