Update: 将子项目从 submodule 转为完整内容

- 移除 GovAI, nomifun-tauri, 算力盒子 的 submodule 引用
- 添加所有子项目的完整源代码
- 保留原始 .git 为 .git.bak 备份

GovAI/server/migrations/000017_drop_conversations_messages.down.sql

@@ -0,0 +1,24 @@
+-- 回滚：重新创建 conversations 表
+CREATE TABLE IF NOT EXISTS conversations (
+    id UUID PRIMARY KEY DEFAULT gen_random_uuid(),
+    app_id UUID NOT NULL REFERENCES applications(id) ON DELETE CASCADE,
+    user_id UUID NOT NULL REFERENCES users(id) ON DELETE CASCADE,
+    title VARCHAR(500),
+    created_at TIMESTAMP WITH TIME ZONE DEFAULT CURRENT_TIMESTAMP,
+    updated_at TIMESTAMP WITH TIME ZONE DEFAULT CURRENT_TIMESTAMP
+);
+
+-- 回滚：重新创建 messages 表
+CREATE TABLE IF NOT EXISTS messages (
+    id UUID PRIMARY KEY DEFAULT gen_random_uuid(),
+    conversation_id UUID NOT NULL REFERENCES conversations(id) ON DELETE CASCADE,
+    role VARCHAR(20) NOT NULL CHECK (role IN ('user', 'assistant', 'system')),
+    content TEXT NOT NULL,
+    created_at TIMESTAMP WITH TIME ZONE DEFAULT CURRENT_TIMESTAMP
+);
+
+-- 回滚：创建索引
+CREATE INDEX IF NOT EXISTS idx_conversations_app_id ON conversations(app_id);
+CREATE INDEX IF NOT EXISTS idx_conversations_user_id ON conversations(user_id);
+CREATE INDEX IF NOT EXISTS idx_messages_conversation_id ON messages(conversation_id);
+CREATE INDEX IF NOT EXISTS idx_messages_created_at ON messages(created_at);