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

tests/test_main_module.py

@@ -0,0 +1,30 @@
+import subprocess
+import sys
+
+from nato_phonetic_alphabet import constants
+
+
+def _run_module(stdin_text: str) -> subprocess.CompletedProcess[str]:
+    return subprocess.run(
+        [sys.executable, "-m", "nato_phonetic_alphabet"],
+        input=stdin_text,
+        capture_output=True,
+        text=True,
+        check=False,
+        timeout=30,
+    )
+
+
+def test_python_dash_m_spells_word_from_piped_input() -> None:
+    result = _run_module("Hi\n")
+
+    assert result.returncode == 0
+    assert constants.RESULT_TEXT in result.stdout
+    assert result.stdout.splitlines()[-2:] == ["Hotel", "India"]
+
+
+def test_python_dash_m_exits_cleanly_on_end_of_input() -> None:
+    result = _run_module("")
+
+    assert result.returncode == 0
+    assert result.stderr == ""