MIL-001: project foundation

pyproject.toml (Python >=3.13, no runtime dependencies, speech and dev extras),
Python .gitignore, layer skeleton with constants.py, Doxyfile, README with the
.venv instructions, the Malay to Danish word list and review record RC-023.

Task: MIL-001#1
Task: MIL-001#2
Task: MIL-001#3
Task: MIL-001#4
Task: MIL-001#5
Task: MIL-001#6

src/flash_card/application/__init__.py

@@ -0,0 +1,5 @@
+"""Application layer: use cases and ports.
+
+@file __init__.py
+@brief Holds use cases and the ports they need; may import only the domain layer.
+"""