feat(agents): Phase 7-10 hook system, plugins, skills, orchestration

Phase 7: Built-in Hooks (audit_log, dangerous_confirmation, security_scan)
Phase 8: Plugin system (PluginManager, PluginSandbox, PluginManifest)
Phase 9: Skills registry (SkillRegistry, local/plugin/MCP loaders)
Phase 10: TeamLeader, RemoteTransport, BackgroundTaskManager

backend/app/agents/skills/__init__.py

@@ -0,0 +1,16 @@
+"""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",
+]