Load skills from classpath (skills jars)

[arefbehboudi]

• Add classpath-based skills loading via agent.skills.paths (e.g. classpath:/META-INF/skills)
• Wire SkillsTool to load both workspace/skills and skills resources
• Add SkillsJarSupportTest to verify loading SKILL.md from a jar on the classpath
• Update README with short setup instructions

Closes #31