docs: add OpenCode and GitHub Copilot CLI platform details

[tylerwillis]

Summary

• Added OpenCode to the supported platforms table with command format (Markdown) and hooks support (No)
• Updated GitHub Copilot CLI entry with command format (Markdown) and hooks support (tool permissions only)

Based on research of both platforms' documentation:

• OpenCode: Uses Markdown files in .opencode/command/, no lifecycle hooks
• GitHub Copilot CLI: Uses Markdown agents in .github/agents/, has tool permissions but no pre/post execution hooks

Test plan

• Verify table renders correctly in README

🤖 Generated with Claude Code

[tylerwillis]

@nhorton fyi - I asked claude to research hook availability and command format, but I haven't yet validated whether the information there is correct. Here's the output on the research:

Key Findings

OpenCode:

• Commands stored in .opencode/command/ as Markdown files
• Similar pattern to Claude Code (filename = command name)
• No hooks/lifecycle events - commands execute synchronously
• Has agents system with permission controls but no pre/post execution hooks

GitHub Copilot CLI:

• Custom agents in .github/agents/ as Markdown with YAML frontmatter
• Tool permissions (--allow-tool, --deny-tool) provide some control
• No lifecycle hooks - known issues where git hooks cause agent to fail
• MCP server support for extensibility but not command-level hooks

Both platforms use Markdown for commands but neither has the rich hooks system that Claude Code offers (stop_hooks, pre_tool_execution, post_tool_execution).

Here are the source URLs from the research:

OpenCode:

• https://opencode.ai/docs/commands/ - Custom commands documentation
• https://opencode.ai/docs/agents/ - Agents configuration
• https://opencode.ai/docs/config/ - Configuration options
• https://github.com/opencode-ai/opencode - GitHub repo/README

GitHub Copilot CLI:

• https://docs.github.com/en/copilot/how-tos/use-copilot-agents/use-copilot-cli - Official CLI docs
• https://jimmysong.io/blog/github-copilot-cli-custom-agents/ - Custom agents guide
• https://github.com/orgs/community/discussions/167906 - Hooks issues discussion
• https://github.blog/changelog/2025-10-28-github-copilot-cli-use-custom-agents-and-delegate-to-copilot-coding-agent/ - Changelog on custom agents