fix: handle multiline YAML block scalars in frontmatter parser

[themavik]

Summary

_parse_frontmatter() in s05_skill_loading.py fails to parse YAML block scalar descriptions (using | or >) in SKILL.md files, resulting in the description being read as just | instead of the actual multiline content.

Problem

The agent-builder/SKILL.md uses a YAML block scalar for its description:

---
name: agent-builder
description: |
  Design and build AI agents for any domain. Use when users:
  (1) ask to "create an agent"...
---

The current parser splits each line independently on :, so description: | produces description → "|". The indented continuation lines are either ignored (no :) or misinterpreted.

Root cause

The line-by-line split(":", 1) approach has no concept of multiline YAML values. It cannot accumulate indented continuation lines that belong to a block scalar key.

Fix

Rewrite _parse_frontmatter() to:

1. Track the current key being parsed
2. When a value is | or >, enter block scalar mode
3. Accumulate indented continuation lines into the current key's value
4. Flush the accumulated value when a new top-level key is encountered

Single-line values (description: Process PDF files) continue to work as before.

Testing

• skills/agent-builder/SKILL.md (block scalar |): description correctly parsed as multiline string
• skills/pdf/SKILL.md (inline value): description parsed correctly (unchanged behavior)
• skills/code-review/SKILL.md (inline value with colons): description parsed correctly

Closes #79

[vercel]

@themavik is attempting to deploy a commit to the crazyboym's projects Team on Vercel.

A member of the Team first needs to authorize it.