[Bug] mac envPaths should match Linux and use ~/.config/opencode/

[jchuder]

Summary: On macOS, envPaths currently resolves to ~/Library/Preferences/opencode/skills/, which breaks config read/write.
The correct path should match Linux and use ~/.config/opencode/. (Base on OpenCode's doc - Global Config)

Background

• Source: src/config.ts
• Current behavior for macOS (darwin): ["~/Library/Preferences/opencode/skills/", ".config/opencode/.opencode/skills"],
• Intended behavior: use path: ~/.config/opencode/ (same as Linux)

Impact

• Actual: Config files are read under ~/Library/Preferences/opencode/skills/ on macOS, causing missing configs and path inconsistencies across platforms.
• Expected: macOS should use ~/.config/opencode/ so Linux/macOS share the same config location.

Steps to Reproduce

1. Run the app on macOS.
2. Trigger any code path that reads/writes config via envPaths.
3. Observe files under ~/Library/Preferences/opencode/skills/ instead of ~/.config/opencode/.

Environment

• OS: macOS (Tahoe 26.2)