MIL-002 NATO converter: modelling, converter code, tests and Doxygen comments

User story, use case and SSD for "spell a word"; spell_word with
try/except KeyError, generate_phonetic with the retry loop, console and CSV
adapters, 49 pytest tests; MIL-002 and the modelling documents accepted with
review records.

Task: MIL-002#1
Task: MIL-002#2
Task: MIL-002#3
Task: MIL-002#4
Task: MIL-002#5
Task: MIL-002#6

src/nato_phonetic_alphabet/application/ports.py

@@ -0,0 +1,30 @@
+"""@brief Ports the use case needs from the outside world."""
+
+from typing import Protocol
+
+
+class InputClosedError(Exception):
+    """@brief Raised when the user can give no more input (end of input, abort)."""
+
+
+class WordConsole(Protocol):
+    """@brief Port for the conversation with the user."""
+
+    def ask_word(self) -> str:
+        """@brief Ask the user for a word.
+
+        @return The word as typed.
+        @throws InputClosedError The user can give no more input.
+        """
+        ...
+
+    def show_invalid(self) -> None:
+        """@brief Tell the user that the word was rejected."""
+        ...
+
+    def show_code_words(self, code_words: list[str]) -> None:
+        """@brief Show the result to the user.
+
+        @param code_words The code words to show.
+        """
+        ...