feat: scaffold FastAPI backend with ports-and-adapters layout

backend/pyproject.toml

@@ -0,0 +1,37 @@
+[project]
+name = "discovery-backend"
+version = "0.1.0"
+description = "LLM-driven music discovery on the Spotify Web API"
+requires-python = "==3.13.*"
+dependencies = [
+    "fastapi>=0.116",
+    "pydantic-settings>=2.10",
+    "uvicorn[standard]>=0.35",
+]
+
+[dependency-groups]
+dev = [
+    "httpx2>=0.1",
+    "mypy>=1.17",
+    "pytest>=8.4",
+    "ruff>=0.12",
+]
+
+[tool.ruff]
+line-length = 100
+target-version = "py313"
+
+[tool.ruff.lint]
+select = ["E", "F", "I", "N", "UP", "B", "SIM", "RUF"]
+
+[tool.mypy]
+python_version = "3.13"
+strict = false
+warn_unused_ignores = true
+
+[[tool.mypy.overrides]]
+module = ["app.domain.*", "app.ports.*", "app.pipeline.*"]
+strict = true
+
+[tool.pytest.ini_options]
+testpaths = ["tests"]