feat: add vers docker run command to execute Dockerfiles on Vers VMs

[yevbar]

Summary

Adds a new vers docker command group that allows running Dockerfiles on Vers VMs instead of containers.

New Commands

• vers docker run [dockerfile] - Parse and execute a Dockerfile on a Vers VM
• vers docker build [context] - Build a Dockerfile as a Vers snapshot (commit)
• vers docker compose up - Start a compose project with each service as a VM

Deprecation Notice

⚠️ vers build --dockerfile is now deprecated in favor of vers docker build.

The old command still works but will show a deprecation warning:

$ vers build --dockerfile ./Dockerfile
Flag --dockerfile has been deprecated, use 'vers docker build -f <dockerfile>' instead
⚠️  DEPRECATED: 'vers build --dockerfile' is deprecated. Use 'vers docker build' instead.

Migration: Replace vers build --dockerfile ./Dockerfile with vers docker build -f ./Dockerfile .

Features

Dockerfile Parsing

• Parses standard Dockerfile instructions: FROM, RUN, COPY, ADD, WORKDIR, ENV, EXPOSE, CMD, ENTRYPOINT
• Handles JSON array format ["cmd", "arg"] and shell format
• Supports line continuations with \
• Multi-stage build support (uses final stage)

Execution

• Creates a new Vers VM with configurable resources
• Copies build context to the VM via SFTP (respects COPY instructions)
• Executes RUN commands sequentially over SSH
• Sets up environment variables from ENV instructions
• Starts the application (CMD/ENTRYPOINT)

Flags

• -d, --detach - Run in background mode
• -i, --interactive - Run with TTY support
• -c, --context - Custom build context directory
• -N, --name - Set VM alias
• -e, --env - Pass additional environment variables
• --mem - Memory size in MiB (default: 1024)
• --vcpu - Number of vCPUs (default: 2)
• --fs-size - Filesystem size in MiB (default: 4096)

Usage Examples

# Build a Dockerfile as a Vers snapshot
vers docker build .
vers docker build -t myapp:latest .
vers docker build -f Dockerfile.prod .

# Run Dockerfile in current directory
vers docker run

# Run specific Dockerfile with custom context
vers docker run -c ./app ./Dockerfile

# Run in detached mode with alias
vers docker run -d -N myapp ./Dockerfile

# Run with custom resources
vers docker run --mem 2048 --vcpu 4 ./Dockerfile

Benefits over Docker

The VM persists after completion, enabling:

• vers connect <vm> - SSH into the environment
• vers commit <vm> - Create a snapshot
• vers branch <vm> - Branch the state
• vers tunnel <vm> <port> - Forward ports

Testing

• Added comprehensive unit tests for Dockerfile parser
• All existing tests pass

Files Changed

• cmd/docker.go - CLI command definitions
• cmd/build.go - Added deprecation for --dockerfile flag
• internal/docker/parser.go - Dockerfile parser
• internal/docker/parser_test.go - Parser tests
• internal/docker/executor.go - Dockerfile executor
• internal/handlers/docker_run.go - Handler logic
• internal/handlers/docker_build.go - Build handler logic
• internal/presenters/docker_presenter.go - Output formatting