Phase 2: Implement Execution Environment Abstraction (v0.3.0)

This commit implements Phase 2 of the CHORUS Task Execution Engine development plan,
providing a comprehensive execution environment abstraction layer with Docker
container sandboxing support.

## New Features

### Core Sandbox Interface
- Comprehensive ExecutionSandbox interface with isolated task execution
- Support for command execution, file I/O, environment management
- Resource usage monitoring and sandbox lifecycle management
- Standardized error handling with SandboxError types and categories

### Docker Container Sandbox Implementation
- Full Docker API integration with secure container creation
- Transparent repository mounting with configurable read/write access
- Advanced security policies with capability dropping and privilege controls
- Comprehensive resource limits (CPU, memory, disk, processes, file handles)
- Support for tmpfs mounts, masked paths, and read-only bind mounts
- Container lifecycle management with proper cleanup and health monitoring

### Security & Resource Management
- Configurable security policies with SELinux, AppArmor, and Seccomp support
- Fine-grained capability management with secure defaults
- Network isolation options with configurable DNS and proxy settings
- Resource monitoring with real-time CPU, memory, and network usage tracking
- Comprehensive ulimits configuration for process and file handle limits

### Repository Integration
- Seamless repository mounting from local paths to container workspaces
- Git configuration support with user credentials and global settings
- File inclusion/exclusion patterns for selective repository access
- Configurable permissions and ownership for mounted repositories

### Testing Infrastructure
- Comprehensive test suite with 60+ test cases covering all functionality
- Docker integration tests with Alpine Linux containers (skipped in short mode)
- Mock sandbox implementation for unit testing without Docker dependencies
- Security policy validation tests with read-only filesystem enforcement
- Resource usage monitoring and cleanup verification tests

## Technical Details

### Dependencies Added
- github.com/docker/docker v28.4.0+incompatible - Docker API client
- github.com/docker/go-connections v0.6.0 - Docker connection utilities
- github.com/docker/go-units v0.5.0 - Docker units and formatting
- Associated Docker API dependencies for complete container management

### Architecture
- Interface-driven design enabling multiple sandbox implementations
- Comprehensive configuration structures for all sandbox aspects
- Resource usage tracking with detailed metrics collection
- Error handling with retryable error classification
- Proper cleanup and resource management throughout sandbox lifecycle

### Compatibility
- Maintains backward compatibility with existing CHORUS architecture
- Designed for future integration with Phase 3 Core Task Execution Engine
- Extensible design supporting additional sandbox implementations (VM, process)

This Phase 2 implementation provides the foundation for secure, isolated task
execution that will be integrated with the AI model providers from Phase 1
in the upcoming Phase 3 development.

🤖 Generated with [Claude Code](https://claude.ai/code)

Co-Authored-By: Claude <noreply@anthropic.com>

vendor/github.com/distribution/reference/MAINTAINERS

@@ -0,0 +1,26 @@
+# Distribution project maintainers & reviewers
+#
+# See GOVERNANCE.md for maintainer versus reviewer roles
+#
+# MAINTAINERS (cncf-distribution-maintainers@lists.cncf.io)
+# GitHub ID, Name, Email address
+"chrispat","Chris Patterson","chrispat@github.com"
+"clarkbw","Bryan Clark","clarkbw@github.com"
+"corhere","Cory Snider","csnider@mirantis.com"
+"deleteriousEffect","Hayley Swimelar","hswimelar@gitlab.com"
+"heww","He Weiwei","hweiwei@vmware.com"
+"joaodrp","João Pereira","jpereira@gitlab.com"
+"justincormack","Justin Cormack","justin.cormack@docker.com"
+"squizzi","Kyle Squizzato","ksquizzato@mirantis.com"
+"milosgajdos","Milos Gajdos","milosthegajdos@gmail.com"
+"sargun","Sargun Dhillon","sargun@sargun.me"
+"wy65701436","Wang Yan","wangyan@vmware.com"
+"stevelasker","Steve Lasker","steve.lasker@microsoft.com"
+#
+# REVIEWERS
+# GitHub ID, Name, Email address
+"dmcgowan","Derek McGowan","derek@mcgstyle.net"
+"stevvooe","Stephen Day","stevvooe@gmail.com"
+"thajeztah","Sebastiaan van Stijn","github@gone.nl"
+"DavidSpek", "David van der Spek", "vanderspek.david@gmail.com"
+"Jamstah", "James Hewitt", "james.hewitt@gmail.com"