feat(dev): add Linux dev container

[Zoupers]

Summary

• add a Linux Dev Container that lets Intel macOS contributors install the locked PyTorch CPU wheel
• cache Python and Playwright dependencies in the image and install the source checkout during postCreate
• provide Python 3.13, uv, Node.js 24, Chromium, FFmpeg, and forwarded API/Explore Lab ports
• document the workflow and its macOS/Tauri limitations in Chinese and English
• lock the Dev Container Node feature to the verified digest

Validation

• jq empty .devcontainer/devcontainer.json
• jq empty .devcontainer/devcontainer-lock.json
• git diff --check
• docker buildx build --check -f .devcontainer/Dockerfile .
• docker buildx build --load -t coworker-devcontainer:test -f .devcontainer/Dockerfile .
• npx -y @devcontainers/cli build --workspace-folder . --image-name coworker-devcontainer:full-test
• verified the full image reports Python 3.13.5, Node.js 24.18.0, uv 0.11.32, and torch 2.11.0+cpu on Linux x86_64
• verified uv sync --frozen --dev succeeds as the non-root vscode user with the source checkout mounted
• uv run --frozen python scripts/check_version.py passes inside the Linux container

Risks and compatibility

• the first container build downloads the locked Python dependencies and Playwright Chromium, so it is relatively large
• the container follows the host architecture: Intel macOS uses Linux x86_64 and Apple Silicon uses Linux arm64
• the Linux container cannot build or validate macOS-specific Tauri artifacts, signing, or notarization
• no runtime, API, security, or migration behavior changes

Checks not run

• the full Python, Rust, and frontend test suites were not run because this change is limited to development-environment configuration and documentation
• the host-side version check cannot resolve dependencies on Intel macOS because PyTorch 2.11.0 has no macOS x86_64 wheel; this is the issue the container addresses