feat(database): add PostgreSQL repository and migration scripts

- Implement PostgresUserRepository with full CRUD operations
- Support all query methods (by_id/email/username/token)
- Use psycopg2 with RealDictCursor for clean mapping
- Create initial schema migration (users/workspaces/members/invitations)
- Add database indexes for performance
- Setup foreign key constraints for data integrity
- Include migration guide and rollback instructions
- Add psycopg2 dependency

Phase 4 Task 28/68 completed

migrations/001_initial_schema.sql

@@ -0,0 +1,87 @@
+"""
+数据库迁移脚本 - 初始化表结构
+"""
+
+-- 用户表
+CREATE TABLE IF NOT EXISTS users (
+    id VARCHAR(255) PRIMARY KEY,
+    email VARCHAR(255) UNIQUE NOT NULL,
+    display_name VARCHAR(255) NOT NULL,
+    username VARCHAR(255) UNIQUE,
+    password_hash VARCHAR(255),
+    email_verified BOOLEAN DEFAULT FALSE,
+    email_verification_token VARCHAR(255),
+    password_reset_token VARCHAR(255),
+    password_reset_expires_at TIMESTAMP,
+    last_login_at TIMESTAMP,
+    last_login_ip VARCHAR(50),
+    created_at TIMESTAMP NOT NULL DEFAULT NOW()
+);
+
+CREATE INDEX idx_users_email ON users(email);
+CREATE INDEX idx_users_username ON users(username);
+CREATE INDEX idx_users_email_verification_token ON users(email_verification_token);
+CREATE INDEX idx_users_password_reset_token ON users(password_reset_token);
+
+
+-- 工作空间表
+CREATE TABLE IF NOT EXISTS workspaces (
+    id VARCHAR(255) PRIMARY KEY,
+    name VARCHAR(255) NOT NULL,
+    owner_user_id VARCHAR(255) NOT NULL REFERENCES users(id) ON DELETE CASCADE,
+    subscription_plan VARCHAR(50) DEFAULT 'free',
+    subscription_status VARCHAR(50) DEFAULT 'active',
+    subscription_expires_at TIMESTAMP,
+    max_projects INTEGER DEFAULT 3,
+    max_storage_gb INTEGER DEFAULT 10,
+    used_storage_gb DECIMAL(10, 2) DEFAULT 0,
+    created_at TIMESTAMP NOT NULL DEFAULT NOW()
+);
+
+CREATE INDEX idx_workspaces_owner ON workspaces(owner_user_id);
+
+
+-- 工作空间成员表
+CREATE TABLE IF NOT EXISTS workspace_members (
+    id VARCHAR(255) PRIMARY KEY,
+    workspace_id VARCHAR(255) NOT NULL REFERENCES workspaces(id) ON DELETE CASCADE,
+    user_id VARCHAR(255) NOT NULL REFERENCES users(id) ON DELETE CASCADE,
+    role VARCHAR(50) NOT NULL,
+    invited_by VARCHAR(255) REFERENCES users(id),
+    joined_at TIMESTAMP NOT NULL DEFAULT NOW(),
+    UNIQUE(workspace_id, user_id)
+);
+
+CREATE INDEX idx_workspace_members_workspace ON workspace_members(workspace_id);
+CREATE INDEX idx_workspace_members_user ON workspace_members(user_id);
+
+
+-- 工作空间邀请表
+CREATE TABLE IF NOT EXISTS workspace_invitations (
+    id VARCHAR(255) PRIMARY KEY,
+    workspace_id VARCHAR(255) NOT NULL REFERENCES workspaces(id) ON DELETE CASCADE,
+    inviter_user_id VARCHAR(255) NOT NULL REFERENCES users(id) ON DELETE CASCADE,
+    invitee_email VARCHAR(255) NOT NULL,
+    role VARCHAR(50) NOT NULL,
+    invitation_token VARCHAR(255) UNIQUE NOT NULL,
+    status VARCHAR(50) DEFAULT 'pending',
+    expires_at TIMESTAMP,
+    accepted_at TIMESTAMP,
+    created_at TIMESTAMP NOT NULL DEFAULT NOW()
+);
+
+CREATE INDEX idx_invitations_workspace ON workspace_invitations(workspace_id);
+CREATE INDEX idx_invitations_token ON workspace_invitations(invitation_token);
+CREATE INDEX idx_invitations_workspace_email ON workspace_invitations(workspace_id, invitee_email, status);
+
+
+-- 项目表（占位，后续 Phase 完善）
+CREATE TABLE IF NOT EXISTS projects (
+    id VARCHAR(255) PRIMARY KEY,
+    workspace_id VARCHAR(255) NOT NULL REFERENCES workspaces(id) ON DELETE CASCADE,
+    name VARCHAR(255) NOT NULL,
+    description TEXT,
+    created_at TIMESTAMP NOT NULL DEFAULT NOW()
+);
+
+CREATE INDEX idx_projects_workspace ON projects(workspace_id);