Replace Claude configuration with OpenCode setup (#151)

* Replace Claude configuration with OpenCode setup

- Remove .claude/ directory (commands and settings)
- Add .opencode/ configuration (agents, commands, skills)
- Add trees/ directory for git worktrees

* Enhance reviewer and command documentation

- Update reviewer.md to include new permissions for GitHub commands and introduce modes for code review (Review & File, Dry Run).
- Revise create-git-worktree.md to clarify execution steps and emphasize the one-shot nature of the command.
- Improve fix-issue.md to streamline the process of validating and fixing GitHub issues, including detailed steps for creating a worktree and reporting results.
- Update SKILL.md for create-git-worktree to better describe its purpose and usage in isolated development environments.

Author: erskingardner