Set up the project skeleton (MIL-001)

pyproject.toml (Python >=3.13, no runtime dependencies, pytest as dev extra),
Python .gitignore, .env.example, constants.py, assignment data files,
Doxyfile and a smoke test.

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

pyproject.toml

@@ -0,0 +1,22 @@
+[build-system]
+requires = ["setuptools>=68"]
+build-backend = "setuptools.build_meta"
+
+[project]
+name = "birthday-wisher"
+version = "0.1.0"
+description = "Sends a random birthday letter by e-mail to everyone whose birthday is today (Udemy 100 Days of Code, day 32)."
+readme = "README.md"
+requires-python = ">=3.13"
+license = { file = "LICENSE" }
+dependencies = []
+
+[project.optional-dependencies]
+dev = ["pytest>=8"]
+
+[tool.setuptools.packages.find]
+where = ["src"]
+
+[tool.pytest.ini_options]
+pythonpath = ["src"]
+testpaths = ["tests"]