feat: add OpenCode integration support

[D36u99er]

Summary

This PR adds support for OpenCode (https://github.com/anomalyco/opencode) as a new agent flavor, enabling mobile control of OpenCode AI terminals through the Happy app.

Key Changes

• New happy opencode subcommand - Start OpenCode sessions with mobile control
• HTTP/SSE API Client - Clean integration using OpenCode's native REST API (port 4096), unlike Claude/Codex PTY spawning
• Real-time event streaming - SSE-based message synchronization for tool calls, reasoning, and todos
• Permission system integration - Forward permission requests to mobile app with full reply options
• Model/Provider selection - Support --model and --provider flags for model configuration

Files Added

src/opencode/
├── index.ts              # Module exports
├── types.ts              # TypeScript type definitions for OpenCode API
├── openCodeClient.ts     # HTTP/SSE client for OpenCode server
├── runOpenCode.ts        # Main entry point (similar to runClaude.ts)
├── messageMapper.ts      # Message format conversion (Happy <-> OpenCode)
└── utils/
    └── permissionHandler.ts  # Permission request handling

Usage

# Start with default settings
happy opencode

# Start with all permissions bypassed
happy opencode --yolo

# Use specific model
happy opencode -m gpt-4o -p openrouter

# Show help
happy opencode --help

Why OpenCode?

OpenCode provides:

• Native HTTP API (cleaner than PTY-based integration)
• Best-in-class context management
• Support for multiple AI providers (OpenRouter, Anthropic, OpenAI, etc.)
• Active development (52k+ stars)

Related

• Feature Request: [Feature Request] Add OpenCode support - from a team spending ~$20k/day on API happy#344
• OpenCode: https://github.com/anomalyco/opencode

Testing

• TypeScript compilation passes
• Build succeeds
• OpenCode API connectivity verified locally