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/devcontainer.json

@@ -0,0 +1,36 @@
+{
+  "name": "kirche-einfach",
+  "build": {
+    "dockerfile": "Dockerfile",
+    "args": {
+      "FORGEJO_USERNAME": "jonas"
+    }
+  },
+  "mounts": [
+    "source=${localEnv:USERPROFILE}/.ssh,target=/mnt/host-ssh,type=bind,readonly",
+    "source=kirche-einfach-venv,target=/workspaces/kirche-einfach/backend/.venv,type=volume",
+    "source=kirche-einfach-node-modules,target=/workspaces/kirche-einfach/frontend/node_modules,type=volume"
+  ],
+  "remoteUser": "vscode",
+  "containerEnv": {
+    "FORGEJO_USERNAME": "jonas"
+  },
+  "overrideCommand": false,
+  "workspaceFolder": "/workspaces/kirche-einfach",
+  "postCreateCommand": "sudo -E bash .devcontainer/setup.sh",
+  "postStartCommand": "mkdir -p ~/.ssh && cp /mnt/host-ssh/id_rsa /mnt/host-ssh/id_rsa.pub ~/.ssh/ && cp /mnt/host-ssh/known_hosts ~/.ssh/ 2>/dev/null; ssh-keyscan -t ed25519,rsa gitlab.jonas-miederer.com >> ~/.ssh/known_hosts 2>/dev/null; chmod 700 ~/.ssh && chmod 600 ~/.ssh/id_rsa && chmod 644 ~/.ssh/id_rsa.pub ~/.ssh/known_hosts",
+  "customizations": {
+    "vscode": {
+      "extensions": [
+        "ms-python.python",
+        "ms-python.vscode-pylance",
+        "charliermarsh.ruff",
+        "dbaeumer.vscode-eslint",
+        "esbenp.prettier-vscode"
+      ],
+      "settings": {
+        "python.defaultInterpreterPath": "/workspaces/kirche-einfach/backend/.venv/bin/python"
+      }
+    }
+  }
+}