resolveSkillPathReferences: add looksLikeFilePath() guard that requires
a file extension or trailing slash before resolving @scope/package
references. npm packages like @mycom/my_mcp_tools@beta were incorrectly
being rewritten to absolute paths in skill templates.
2 new tests.
Skill loaders previously only told agents that @path references are
relative to the skill directory, but agents often failed to resolve
them. Now @path/with/slash patterns are automatically expanded to
absolute paths during template construction.
YeonGyu-Kim