feat: 添加PostgreSQL支持并更新数据库配置

- 新增PostgreSQL服务支持，使用最新版17
- 更新Docker Compose配置以支持PostgreSQL和Redis
- 修改数据库连接逻辑，支持PostgreSQL和SQLite
- 更新文档以反映新的数据库配置和使用方法
- 优化数据模型，确保时间戳字段支持时区

api/database/models.py

@@ -1,7 +1,7 @@
 """
 数据库模型定义
 """
-from datetime import datetime
+from datetime import datetime, timezone
 from typing import Optional, List
 from sqlalchemy import Column, String, Integer, DateTime, Boolean, Text, ForeignKey, JSON
 from sqlalchemy.ext.declarative import declarative_base
@@ -10,6 +10,11 @@ from sqlalchemy.orm import relationship
 Base = declarative_base()
 
 
+def utc_now():
+    """返回当前 UTC 时间（带时区信息）"""
+    return datetime.now(timezone.utc)
+
+
 class User(Base):
     """用户表"""
     __tablename__ = "users"
@@ -22,7 +27,7 @@ class User(Base):
     nickname = Column(String, nullable=False)
     avatar_url = Column(String, nullable=True)
     subscription_type = Column(String, default="free")  # free, premium
-    created_at = Column(DateTime, default=datetime.utcnow)
+    created_at = Column(DateTime(timezone=True), default=utc_now)
 
     # Relationships
     conversations = relationship("Conversation", back_populates="user")
@@ -38,8 +43,8 @@ class Conversation(Base):
 
     id = Column(String, primary_key=True)
     user_id = Column(String, ForeignKey("users.id"), nullable=False)
-    started_at = Column(DateTime, default=datetime.utcnow)
-    ended_at = Column(DateTime, nullable=True)
+    started_at = Column(DateTime(timezone=True), default=utc_now)
+    ended_at = Column(DateTime(timezone=True), nullable=True)
     duration_seconds = Column(Integer, default=0)
     summary = Column(Text, nullable=True)
     status = Column(String, default="active")  # active, ended, processing
@@ -59,7 +64,7 @@ class Segment(Base):
     conversation_id = Column(String, ForeignKey("conversations.id"), nullable=False)
     audio_url = Column(String, nullable=True)
     transcript_text = Column(Text, nullable=False)
-    created_at = Column(DateTime, default=datetime.utcnow)
+    created_at = Column(DateTime(timezone=True), default=utc_now)
     processed = Column(Boolean, default=False)
     topic_category = Column(String, nullable=True)
     agent_response = Column(Text, nullable=True)
@@ -79,7 +84,7 @@ class Chapter(Base):
     order_index = Column(Integer, nullable=False)
     status = Column(String, default="draft")  # draft, completed
     images = Column(JSON, nullable=True)  # 图片 URL 列表
-    updated_at = Column(DateTime, default=datetime.utcnow, onupdate=datetime.utcnow)
+    updated_at = Column(DateTime(timezone=True), default=utc_now, onupdate=utc_now)
     category = Column(String, nullable=True)  # 章节分类
     is_new = Column(Boolean, default=True)  # 是否为新内容（未读）
     source_segments = Column(JSON, nullable=True)  # 来源 segment IDs 列表
@@ -98,7 +103,7 @@ class Book(Base):
     total_pages = Column(Integer, default=0)
     total_words = Column(Integer, default=0)
     cover_image_url = Column(String, nullable=True)
-    updated_at = Column(DateTime, default=datetime.utcnow, onupdate=datetime.utcnow)
+    updated_at = Column(DateTime(timezone=True), default=utc_now, onupdate=utc_now)
     has_update = Column(Boolean, default=False)  # 是否有新内容
     last_update_chapter_id = Column(String, nullable=True)  # 最近更新的章节 ID
 
@@ -116,7 +121,7 @@ class MemoirState(Base):
     current_stage = Column(String, default="childhood")  # 当前阶段
     covered_stages = Column(JSON, default=list)  # 已完成阶段列表
     slots = Column(JSON, nullable=False)  # 各阶段 slot 信息
-    updated_at = Column(DateTime, default=datetime.utcnow, onupdate=datetime.utcnow)
+    updated_at = Column(DateTime(timezone=True), default=utc_now, onupdate=utc_now)
 
     # Relationships
     user = relationship("User", back_populates="memoir_state")
@@ -129,8 +134,8 @@ class RefreshToken(Base):
     id = Column(String, primary_key=True)
     user_id = Column(String, ForeignKey("users.id"), nullable=False, index=True)
     token = Column(String, unique=True, nullable=False, index=True)  # 刷新令牌（唯一）
-    expires_at = Column(DateTime, nullable=False)  # 过期时间（30天后）
-    created_at = Column(DateTime, default=datetime.utcnow)
+    expires_at = Column(DateTime(timezone=True), nullable=False)  # 过期时间（30天后）
+    created_at = Column(DateTime(timezone=True), default=utc_now)
     is_revoked = Column(Boolean, default=False)  # 是否已撤销
 
     # Relationships