Add VS Code devcontainer configuration

.devcontainer/Dockerfile

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+# Use the official Go image as base
+FROM golang:1.25-bookworm
+
+# Install system dependencies
+RUN apt-get update && export DEBIAN_FRONTEND=noninteractive \
+    && apt-get -y install --no-install-recommends \
+        build-essential \
+        ca-certificates \
+        curl \
+        git \
+        gnupg \
+        make \
+        nano \
+        software-properties-common \
+        vim \
+        wget \
+    && apt-get clean -y && rm -rf /var/lib/apt/lists/*
+
+# Install golangci-lint
+RUN curl -sSfL https://raw.githubusercontent.com/golangci/golangci-lint/master/install.sh | sh -s -- -b /usr/local/bin v1.62.2
+
+# Install goreleaser
+RUN echo 'deb [trusted=yes] https://repo.goreleaser.com/apt/ /' | tee /etc/apt/sources.list.d/goreleaser.list \
+    && apt-get update \
+    && apt-get install -y goreleaser \
+    && apt-get clean -y && rm -rf /var/lib/apt/lists/*
+
+# Install Hugo (for documentation)
+RUN wget https://github.com/gohugoio/hugo/releases/download/v0.139.4/hugo_extended_0.139.4_linux-amd64.deb \
+    && dpkg -i hugo_extended_0.139.4_linux-amd64.deb \
+    && rm hugo_extended_0.139.4_linux-amd64.deb
+
+# Create a non-root user
+ARG USERNAME=vscode
+ARG USER_UID=1000
+ARG USER_GID=$USER_UID
+
+RUN groupadd --gid $USER_GID $USERNAME \
+    && useradd --uid $USER_UID --gid $USER_GID -m $USERNAME -s /bin/bash \
+    && apt-get update \
+    && apt-get install -y sudo \
+    && echo $USERNAME ALL=\(root\) NOPASSWD:ALL > /etc/sudoers.d/$USERNAME \
+    && chmod 0440 /etc/sudoers.d/$USERNAME
+
+# Set up Go workspace
+ENV GOPATH=/go
+RUN mkdir -p /go/pkg/mod && chown -R ${USERNAME}:${USERNAME} /go
+
+# Switch to non-root user
+USER $USERNAME
+
+# Install Go tools that are commonly used
+RUN go install golang.org/x/tools/gopls@latest \
+    && go install github.com/go-delve/delve/cmd/dlv@latest \
+    && go install honnef.co/go/tools/cmd/staticcheck@latest
+
+# Set working directory
+WORKDIR /workspace
+
+# Persist bash history across container restarts
+VOLUME ["/home/vscode/.bash_history"]

.devcontainer/README.md

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+# Kosli CLI DevContainer
+
+This devcontainer provides a complete development environment for the Kosli CLI project.
+
+## What's Included
+
+### Languages & Runtimes
+
+- **Go 1.25** - Primary development language
+- **Node.js LTS** - For npm package management and release
+
+### Development Tools
+
+- **golangci-lint** - Go linting and static analysis
+- **goreleaser** - Release automation
+- **gotestsum** - Enhanced Go test runner
+- **Hugo Extended** - Documentation site generation
+- **GitHub CLI (gh)** - GitHub integration
+
+### Infrastructure
+
+- **Docker-in-Docker** - For integration tests (runs Kosli server)
+- **Make** - Build automation
+- **Git** - Version control
+
+## Getting Started
+
+1. **Open in VS Code**
+   - Install the "Dev Containers" extension
+   - Open this repository in VS Code
+   - Click "Reopen in Container" when prompted (or use Command Palette: "Dev Containers: Reopen in Container")
+
+2. **Wait for Setup**
+   - The container will build (first time takes a few minutes)
+   - Post-create commands will run automatically (`go mod download`, etc.)
+
+3. **Start Developing**
+
+   ```bash
+   # Build the CLI
+   make build
+
+   # Run tests
+   make test_integration
+
+   # Run linting
+   make lint
+
+   # Build documentation
+   make hugo-local
+   ```
+
+## Container Features
+
+### Forwarded Ports
+
+- **1515** - Hugo documentation server
+- **8001** - Local Kosli server (for integration tests)
+
+### Volume Mounts
+
+- Go module cache is persisted in a Docker volume for faster builds
+- Docker socket is mounted for Docker-in-Docker functionality
+
+### VS Code Extensions
+
+The following extensions are automatically installed:
+
+- **Go** - Go language support
+- **Docker** - Docker file and container management
+- **GitLens** - Enhanced Git capabilities
+
+### VS Code Settings
+
+Pre-configured with:
+
+- Go formatting on save
+- Automatic import organization
+- golangci-lint integration
+- Go language server (gopls)
+
+## Common Tasks
+
+### Building the CLI
+
+```bash
+make build
+./kosli version
+```
+
+### Running Tests
+
+```bash
+# Integration tests (requires Docker)
+make test_integration
+
+# Run all tests including slow ones
+make test_integration_full
+
+# Run specific test suite
+make test_integration_single TARGET=TestAttestJunitCommandTestSuite
+```
+
+### Working with NPM Package
+
+```bash
+# Test npm package installation locally
+npm install
+npm test
+
+# Pack for distribution
+npm pack
+
+# Test the packed version
+mkdir /tmp/npm-test && cd /tmp/npm-test
+npm install /workspace/*.tgz
+npx kosli version
+```
+
+### Documentation
+
+```bash
+# Generate CLI documentation
+make cli-docs
+
+# Start Hugo documentation server (accessible at localhost:1515)
+make hugo-local
+```
+
+### Linting
+
+```bash
+make lint
+```
+
+## Environment Variables
+
+The following environment variables are pre-configured:
+
+- `CGO_ENABLED=0` - Disable CGO for static binaries
+- `GO111MODULE=on` - Use Go modules
+- `GOPATH=/go` - Go workspace location
+
+### Required for Testing
+
+You need to set `KOSLI_API_TOKEN_PROD` for integration tests:
+
+```bash
+export KOSLI_API_TOKEN_PROD="your-token-here"
+```
+
+## Docker Integration
+
+The devcontainer uses Docker-in-Docker to run integration tests. The Kosli server runs in a container alongside your tests.
+
+### Managing Test Containers
+
+```bash
+# View server logs
+make logs_integration_test_server
+
+# Follow server logs
+make follow_integration_test_server
+
+# Enter server container
+make enter_integration_test_server
+```
+
+## Troubleshooting
+
+### Container won't start
+
+- Ensure Docker Desktop is running
+- Check Docker has enough resources (4GB+ RAM recommended)
+- Try rebuilding: Command Palette → "Dev Containers: Rebuild Container"
+
+### Tests failing
+
+- Ensure `KOSLI_API_TOKEN_PROD` is set
+- Check Docker is working: `docker ps`
+- Verify network: `docker network ls` (should see `cli_net`)
+
+### Go modules issues
+
+```bash
+go clean -modcache
+go mod download
+go mod tidy
+```
+
+### NPM installation issues
+
+```bash
+rm -rf node_modules package-lock.json
+npm install
+```
+
+## Customization
+
+### Adding VS Code Extensions
+
+Edit [.devcontainer/devcontainer.json](.devcontainer/devcontainer.json):
+
+```json
+"extensions": [
+  "golang.go",
+  "your-extension-id"
+]
+```
+
+### Installing Additional Tools
+
+Edit [.devcontainer/Dockerfile](.devcontainer/Dockerfile) and rebuild the container.
+
+### Changing Environment Variables
+
+Edit the `remoteEnv` section in [.devcontainer/devcontainer.json](.devcontainer/devcontainer.json).
+
+## Non-Root User
+
+The container runs as the `vscode` user (non-root) for security. Use `sudo` if you need root access:
+
+```bash
+sudo apt-get install some-package
+```
+
+## References
+
+- [Dev Containers Documentation](https://code.visualstudio.com/docs/devcontainers/containers)
+- [Kosli Documentation](https://docs.kosli.com/)
+- [Project Development Guide](../dev-guide.md)

.devcontainer/devcontainer.json

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+{
+  "name": "Kosli CLI Development",
+  "build": {
+    "dockerfile": "Dockerfile",
+    "context": ".."
+  },
+
+  // Configure tool-specific properties
+  "customizations": {
+    "vscode": {
+      "settings": {
+        "go.gopath": "/go",
+        "go.toolsManagement.checkForUpdates": "local",
+        "go.useLanguageServer": true,
+        "go.lintTool": "golangci-lint",
+        "go.lintOnSave": "workspace",
+        "editor.formatOnSave": true,
+        "[go]": {
+          "editor.defaultFormatter": "golang.go",
+          "editor.codeActionsOnSave": {
+            "source.organizeImports": "explicit"
+          }
+        }
+      },
+      "extensions": [
+        "DavidAnson.vscode-markdownlint",
+        "eamodio.gitlens",
+        "golang.go",
+        "ms-azuretools.vscode-docker",
+        "ms-vscode.makefile-tools",
+        "yzhang.markdown-all-in-one"
+      ]
+    }
+  },
+
+  // Use 'forwardPorts' to make a list of ports inside the container available locally
+  "forwardPorts": [1515, 8001],
+
+  // Use 'postCreateCommand' to run commands after the container is created
+  "postCreateCommand": "go mod download && go install gotest.tools/gotestsum@latest",
+
+  // Features to add to the dev container
+  "features": {
+    "ghcr.io/devcontainers/features/docker-in-docker:2": {
+      "version": "latest",
+      "moby": true,
+      "dockerDashComposeVersion": "v2"
+    },
+    "ghcr.io/devcontainers/features/node:1": {
+      "version": "lts",
+      "nodeGypDependencies": true,
+      "installYarnUsingApt": false
+    },
+    "ghcr.io/devcontainers/features/github-cli:1": {
+      "version": "latest"
+    }
+  },
+
+  // Set environment variables
+  "remoteEnv": {
+    "CGO_ENABLED": "0",
+    "GO111MODULE": "on",
+    "GOPATH": "/go"
+  },
+
+  // Run as vscode user (non-root)
+  "remoteUser": "vscode",
+
+  // Mount docker socket and go module cache
+  "mounts": [
+    "source=/var/run/docker.sock,target=/var/run/docker.sock,type=bind",
+    "source=kosli-cli-gomod,target=/go/pkg/mod,type=volume"
+  ]
+}