feat(dev): add Podman-based container workflow

- Add Containerfile for running Astro dev server in a container
- Add compose.yml (slirp4netns) for WSL2/rootless compatibility
- Document Podman compose usage and troubleshooting steps in README
- Ignore optional Podman env file in .gitignore

Containerfile

@@ -0,0 +1,15 @@
+# syntax=docker/dockerfile:1
+FROM node:lts-bookworm-slim
+
+WORKDIR /app
+
+# Install dependencies first (better layer caching)
+COPY package.json package-lock.json ./
+RUN npm ci
+
+# Copy the rest of the project
+COPY . .
+
+EXPOSE 4321
+
+CMD ["npm","run","dev","--","--host","0.0.0.0","--port","4321"]