fix(nacos-skill): handle block-sequence arrays in SKILL.md frontmatter

[sunwg2]

Nacos exports use multi-line - item syntax for array fields. The old normalizer concatenated items into an invalid scalar, causing SnakeYAML to throw "sequence entries are not allowed here in 'string'".

Collect - item lines into a list and emit them as an inline YAML array ["a", "b"]; strip YAML quoting from raw items via unquoteYamlString().

Closes #1438

AgentScope-Java Version

[The version of AgentScope-Java you are working on, e.g. 1.0.12, check your pom.xml dependency version or run mvn dependency:tree | grep agentscope-parent:pom(only mac/linux)]

Description

Fix #1438 — NacosSkillRepository crashes with
sequence entries are not allowed here in 'string' when a SKILL.md
exported from Nacos uses YAML block-sequence syntax for array fields
such as trigger_intents.

normalizeFoldedFlatYaml() was designed to fold indented continuation
lines back into the previous key's value. It had no awareness of YAML
block-sequence entry lines (- item), so it treated them as plain
continuation text and concatenated all items into a single invalid scalar:

Checklist

Please check the following items before code is ready to be reviewed.

• Code has been formatted with mvn spotless:apply
• All tests are passing (mvn test)
• Javadoc comments are complete and follow project conventions
• Related documentation has been updated (e.g. links, examples, etc.)
• Code is ready for review

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