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/app/settings.py

@@ -0,0 +1,11 @@
+from pydantic_settings import BaseSettings
+
+
+class Settings(BaseSettings):
+    version: str = "0.1.0"
+    debug: bool = False
+
+    model_config = {"env_prefix": "KIRCHE_"}
+
+
+settings = Settings()