YAML parsing errors in skills/agents cause TUI crashes

[vvarp]

Description

When a SKILL.md, command, or agent file contains error in frontmatter YAML portion of markdown file, the TUI crashes with a fullscreen ConfigFrontmatterError that covers the entire interface. In the desktop/web version no error message is being shown.

Example of problematic frontmatter (unquoted : in the description field):

---
name: test-skill
description: Use this skill for testing stuff. Reference: https://example.com
---

Plugins

No response

OpenCode version

latest dev branch

Steps to reproduce

1. Create a skill file at .opencode/skill/test/SKILL.md:

---
name: test-skill
description: Use this skill for testing stuff. Reference: https://example.com
---

2. Run opencode
3. Send any message to see TUI crash with fullscreen ConfigFrontmatterError

Screenshot and/or share link

Notice the error message covering bottom part of TUI:

Operating System

macOS Tahoe

Terminal

Any