fix(skills): use yaml.safe_load for frontmatter parsing to handle multiline descriptions

The hand-rolled line-by-line YAML parser treated each line independently,
so YAML multiline scalars (folded `>` and literal `|`) were captured as
the literal characters ">" or "|" instead of the actual text content.

pyproject.toml

@@ -50,6 +50,7 @@ dependencies = [
     "tiktoken>=0.12.0,<1.0.0",
     "jinja2>=3.1.0,<4.0.0",
     "dulwich>=0.22.0,<1.0.0",
+    "pyyaml>=6.0,<7.0.0",
     "filelock>=3.25.2",
 ]