feat(skills): enhance skills system with matching and evaluation

Ultraworked with [Sisyphus](https://github.com/code-yeongyu/oh-my-openagent)

Co-authored-by: Sisyphus <clio-agent@sisyphuslabs.ai>

backend/app/agents/skills/__init__.py

@@ -1,16 +1 @@
-"""Skills 注册表 - Phase 9"""
-
-from app.agents.skills.registry import SkillRegistry, get_skill_registry
-from app.agents.skills.metadata import SkillMetadata
-from app.agents.skills.loaders.local_loader import LocalSkillLoader
-from app.agents.skills.loaders.plugin_loader import PluginSkillLoader
-from app.agents.skills.mcp_builder import MCPSkillBuilder
-
-__all__ = [
-    "SkillRegistry",
-    "SkillMetadata",
-    "LocalSkillLoader",
-    "PluginSkillLoader",
-    "MCPSkillBuilder",
-    "get_skill_registry",
-]
+"""Skill package."""