for opencode harness users, link the skills instead of injecting AGENTS.md

## Summary Opencode users likely don't want their opencode AGENTS.md injected, this bloats the system prompt for all uses of opencode. A better approach is to use the skills feature as was done with claude code. ## Proposed solution ``` mkdir -p ~/.config/opencode/skills ln -s ~/.agentfield/skills/agentfield/current ~/.config/opencode/skills/agentfield ``` ## Alternatives considered none ## Additional context none