feat: 更新数据库和后端服务

- 新增chat_sessions和chat_groups数据库表
- 更新skill_handler和model相关接口
- 修改main.go注册新路由

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

server/migrations/agent_system.sql

@@ -49,6 +49,48 @@ CREATE INDEX IF NOT EXISTS idx_agent_tasks_created ON agent_tasks(created_at DES
 CREATE INDEX IF NOT EXISTS idx_agent_team_supervisor ON agent_teams(supervisor_agent_id);
 CREATE INDEX IF NOT EXISTS idx_agent_team_member ON agent_teams(member_agent_id);
 
+-- Chat Sessions Table
+CREATE TABLE IF NOT EXISTS chat_sessions (
+    id VARCHAR(36) PRIMARY KEY,
+    user_id VARCHAR(36) NOT NULL,
+    agent_id VARCHAR(36),
+    title VARCHAR(255),
+    model_id VARCHAR(36),
+    status VARCHAR(20) DEFAULT 'active',
+    created_at DATETIME(3),
+    updated_at DATETIME(3),
+    INDEX idx_chat_sessions_user (user_id),
+    INDEX idx_chat_sessions_agent (agent_id),
+    INDEX idx_chat_sessions_updated (updated_at DESC)
+);
+
+-- Chat Messages Table
+CREATE TABLE IF NOT EXISTS chat_messages (
+    id VARCHAR(36) PRIMARY KEY,
+    session_id VARCHAR(36) NOT NULL,
+    role VARCHAR(20),
+    content TEXT,
+    tokens_used INT DEFAULT 0,
+    duration_ms INT DEFAULT 0,
+    metadata TEXT,
+    created_at DATETIME(3),
+    INDEX idx_chat_messages_session (session_id),
+    INDEX idx_chat_messages_created (created_at ASC)
+);
+
+-- Chat Groups Table
+CREATE TABLE IF NOT EXISTS chat_groups (
+    id VARCHAR(36) PRIMARY KEY,
+    user_id VARCHAR(36) NOT NULL,
+    name VARCHAR(100) NOT NULL,
+    description TEXT,
+    agent_ids TEXT,
+    status VARCHAR(20) DEFAULT 'active',
+    created_at DATETIME(3),
+    updated_at DATETIME(3),
+    INDEX idx_chat_groups_user (user_id)
+);
+
 -- Agent Memory Indexes
 CREATE INDEX IF NOT EXISTS idx_agent_memory_agent ON agent_memories(agent_id);
 CREATE INDEX IF NOT EXISTS idx_agent_memory_user ON agent_memories(agent_id, user_id);