feat: initial project setup

- FastAPI backend (Python 3.12, uv)
- React 19 + TypeScript + Vite frontend
- Devcontainer with Node 22, Python 3.12, uv, opencode
- Basic app structure and project docs

backend/pyproject.toml

@@ -0,0 +1,19 @@
+[project]
+name = "kirche-einfach-backend"
+version = "0.1.0"
+description = "Kirche Einfach - KI-gestuetzte Verwaltungsplattform fuer Kirche"
+requires-python = ">=3.12"
+dependencies = [
+    "fastapi[standard]>=0.115.0",
+    "django>=5.1",
+    "pydantic-settings>=2.0",
+    "uvicorn[standard]>=0.30.0",
+]
+
+[build-system]
+requires = ["uv_build>=0.12.3,<0.13"]
+build-backend = "uv_build"
+
+[tool.uv.build-backend]
+module-name = "app"
+module-root = ""