feat: add standalone CLI for cross-agent PTY management

[fcoury]

Summary

This PR adds a standalone CLI tool (pty-skill) that enables any AI agent to manage interactive PTY sessions, not just OpenCode. The CLI works with Claude Code, Codex CLI, and other AI tools without requiring MCP server configuration (which would pollute context on every message).

Motivation

The current plugin only works with OpenCode. Many AI agents (Claude Code, Codex CLI, etc.) need to interact with long-running processes but lack this capability. An MCP server approach was considered but rejected because tool definitions would be included in every message, consuming tokens even when unused.

The CLI + Skill approach solves this:

• Zero context pollution - skill is only loaded on-demand
• Works with any agent that has bash access
• Preserves existing plugin - OpenCode users are unaffected

Changes

Architecture

• Extract shared core (src/core/) from plugin code
• Unix socket daemon for session persistence across CLI calls
• JSON-RPC protocol for client-daemon communication
• Auto-start daemon on first CLI invocation

New Files

• cli/ - Complete CLI implementation (daemon, client, commands)
• src/core/ - Shared core (manager, buffer, types, logger)
• SKILL.md - AI agent skill documentation with triggers
• build-cli.ts - Build script for platform binaries
• examples/claude-code-conversation.md - Real usage example

CLI Commands

pty-skill spawn <cmd> [args...]   # Start background PTY
pty-skill read <id>               # Read output with pagination/filtering
pty-skill write <id> <data>       # Send input (supports escape sequences)
pty-skill list                    # List all sessions
pty-skill kill <id>               # Terminate session
pty-skill status                  # Check daemon status
pty-skill daemon <action>         # Manage daemon

Package Changes

• Renamed to pty-skill (more descriptive for cross-agent use)
• Added bin entry for CLI
• Updated GitHub workflow to build and upload release binaries

Backward Compatibility

• Existing OpenCode plugin continues to work unchanged
• Plugin now imports from shared src/core/ instead of duplicated code

Testing

• Full integration test of spawn → read → write → kill flow
• Tested with Claude Code (see examples/claude-code-conversation.md)

[shekohex]

Cool idea, but I would like to keep this as a plugin only for now, I'm open to have that as a standalone CLI though but could be a separate repo. If you are willing to keep maintaining that, I would mention your repo in this repo's README too :)