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/Dockerfile

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+FROM mcr.microsoft.com/devcontainers/base:debian
+
+ARG FORGEJO_USERNAME
+ENV FORGEJO_USERNAME=${FORGEJO_USERNAME}
+
+# SSH (missing from base image)
+RUN apt-get update \
+    && apt-get install -y --no-install-recommends openssh-client \
+    && rm -rf /var/lib/apt/lists/*
+
+# Node.js 22 + npm (npm tree copied; bin symlinks recreated - COPY dereferences them)
+COPY --from=node:22-slim /usr/local/bin/node /usr/local/bin/
+COPY --from=node:22-slim /usr/local/lib/node_modules /usr/local/lib/node_modules
+RUN ln -s ../lib/node_modules/npm/bin/npm-cli.js /usr/local/bin/npm \
+    && ln -s ../lib/node_modules/npm/bin/npx-cli.js /usr/local/bin/npx
+
+# uv (from distroless)
+COPY --from=ghcr.io/astral-sh/uv:latest /uv /usr/local/bin/uv
+
+# Python 3.12 (system-shared location; default /root is unreadable for vscode)
+ENV UV_PYTHON_INSTALL_DIR=/opt/uv/python
+RUN uv python install 3.12 \
+    && ln -s /opt/uv/python/cpython-3.12-linux-x86_64-gnu/bin/python3.12 /usr/local/bin/python3.12 \
+    && ln -s python3.12 /usr/local/bin/python3 \
+    && ln -s python3 /usr/local/bin/python
+
+# Trust the workspace bind mount (source on Windows FS -> uid mismatch)
+RUN git config --system --add safe.directory /workspaces/kirche-einfach
+
+# Pre-create named-volume targets (volumes inherit image content on first mount)
+RUN mkdir -p /workspaces/kirche-einfach/backend/.venv \
+             /workspaces/kirche-einfach/frontend/node_modules
+
+# opencode (as non-root user)
+USER vscode
+RUN curl -fsSL https://opencode.ai/install | bash
+USER root
+RUN ln -s /home/vscode/.opencode/bin/opencode /usr/local/bin/opencode
+
+# Fix ownership (home + volume targets so vscode user can write)
+RUN chown -R vscode:vscode /home/vscode /workspaces
+
+CMD ["sleep", "infinity"]

.devcontainer/devcontainer.json

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+{
+  "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"
+      }
+    }
+  }
+}

.devcontainer/setup.sh

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+#!/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