Plan project and set up Phase 1 skeleton

Add the framework submodule and the accepted planning documents:
Business Case, Stakeholder Analysis, Project Plan, three milestones,
review records RC-001 to RC-006 and the traceability matrix.

Set up the project skeleton for MIL-001: pyproject.toml (Python
>=3.13, no runtime dependencies, pytest/ruff/mypy as dev extra),
 src/coffee_machine/constants.py, a constants consistency test,
 Doxyfile and a CI workflow that runs ruff, mypy and pytest.

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

src/coffee_machine/constants.py

@@ -0,0 +1,45 @@
+"""! @file
+@brief Constants for the coffee machine: menu, resources, coins and commands.
+"""
+
+from typing import Final
+
+## @name Ingredient names
+## @{
+WATER: Final = "water"
+MILK: Final = "milk"
+COFFEE: Final = "coffee"
+## @}
+
+## @brief Cost in dollars and ingredient amounts per drink.
+MENU: Final[dict[str, dict[str, object]]] = {
+    "espresso": {"cost": 1.5, "ingredients": {WATER: 50, MILK: 0, COFFEE: 18}},
+    "latte": {"cost": 2.5, "ingredients": {WATER: 200, MILK: 150, COFFEE: 24}},
+    "cappuccino": {"cost": 3.0, "ingredients": {WATER: 250, MILK: 100, COFFEE: 24}},
+}
+
+## @brief Amount of each ingredient the machine starts with.
+INITIAL_RESOURCES: Final[dict[str, int]] = {WATER: 300, MILK: 200, COFFEE: 100}
+
+## @brief Units used when reporting each resource.
+RESOURCE_UNITS: Final[dict[str, str]] = {WATER: "ml", MILK: "ml", COFFEE: "g"}
+
+## @brief Value in dollars of each accepted coin.
+COIN_VALUES: Final[dict[str, float]] = {
+    "quarters": 0.25,
+    "dimes": 0.10,
+    "nickels": 0.05,
+    "pennies": 0.01,
+}
+
+## @brief Money in the machine at the start.
+INITIAL_PROFIT: Final = 0.0
+
+## @brief Currency symbol shown in messages.
+CURRENCY: Final = "$"
+
+## @name Commands at the prompt
+## @{
+COMMAND_OFF: Final = "off"
+COMMAND_REPORT: Final = "report"
+## @}