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

.devcontainer/setup.sh

@@ -0,0 +1,23 @@
+#!/bin/bash
+set -e
+
+echo "=== Setting up kirche-einfach ==="
+
+# Backend
+echo "--- Installing Python dependencies ---"
+cd /workspaces/kirche-einfach/backend
+uv sync
+
+# Frontend
+echo "--- Installing Node dependencies ---"
+cd /workspaces/kirche-einfach/frontend
+npm install
+
+echo ""
+echo "=== Setup complete ==="
+echo "Forgejo username: $FORGEJO_USERNAME"
+
+# Hand dirs back to vscode (this script runs via sudo; uv/npm create caches as root)
+chown -R vscode:vscode /workspaces/kirche-einfach/backend/.venv \
+                       /workspaces/kirche-einfach/frontend/node_modules \
+                       /home/vscode/.cache 2>/dev/null || true