refactor: update devcontainer and Biome configuration (#27)

- Remove ESLint and Prettier in favor of Biome
- Configure Biome as default formatter for TS/JS/JSON/MD
- Add development helper extensions
- Update VSCode settings for Biome integration

Closes #27

.devcontainer/Dockerfile

@@ -0,0 +1,12 @@
+FROM mcr.microsoft.com/devcontainers/typescript-node:1-20-bullseye
+
+LABEL org.opencontainers.image.source="https://github.com/acedanger/finance"
+LABEL org.opencontainers.image.description="Dev container for Finance App"
+
+# Install additional OS packages
+RUN apt-get update && export DEBIAN_FRONTEND=noninteractive \
+    && apt-get -y install --no-install-recommends git-core \
+    && apt-get clean -y && rm -rf /var/lib/apt/lists/*
+
+# Install global npm packages if needed
+RUN su node -c "npm install -g typescript"