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

@@ -0,0 +1,43 @@
+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"]