refactor: 移除 PostgreSQL 支持，简化为纯 SQLite 部署

- config.py: DATABASE_URL 默认值改为 SQLite
- database.py: 移除 PostgreSQL 分支，简化为纯 SQLite
- models/base.py: 移除 pgvector 导入和条件分支
- search_service.py: 移除 _search_postgres 方法
- import_service.py: 移除 pgvector 相关代码
- requirements.txt: 移除 asyncpg/alembic/pgvector 依赖
- pyproject.toml: 同步移除相关依赖
- docker-compose.yml: 移除 db 服务，- 删除 alembic.ini/Dockerfile.db/sql 目录
- README.md: 更新文档，移除 PostgreSQL 相关内容

适合 NAS 等资源受限环境的轻量级部署

app/database.py

@@ -1,12 +1,13 @@
 """
-数据库连接模块
-支持 PostgreSQL（生产）和 SQLite（本地开发）两种后端
+数据库连接管理
+
+SQLite 数据库，支持异步操作。
 """
 
 from __future__ import annotations
 
-from collections.abc import AsyncGenerator
 from pathlib import Path
+from typing import AsyncGenerator
 
 from sqlalchemy import text
 from sqlalchemy.ext.asyncio import (
@@ -14,35 +15,25 @@ from sqlalchemy.ext.asyncio import (
     async_sessionmaker,
     create_async_engine,
 )
-from sqlalchemy.pool import NullPool
 
 from app.config import settings
 
-# ──────────────────────────── 判断数据库类型 ────────────────────────────
+# ──────────────────────────── 数据库引擎 ────────────────────────────
 
 DB_URL = settings.DATABASE_URL
-IS_SQLITE = DB_URL.startswith("sqlite")
 
-# ──────────────────────────── 异步引擎 ────────────────────────────
+# 解析 SQLite 文件路径
+sqlite_path = DB_URL.replace("sqlite+aiosqlite:///", "")
+if not sqlite_path.startswith("/"):
+    sqlite_path = str(Path(__file__).parent.parent / sqlite_path)
 
-if IS_SQLITE:
-    # SQLite 配置
-    sqlite_path = DB_URL.replace("sqlite+aiosqlite:///", "")
-    if not sqlite_path.startswith("/"):
-        sqlite_path = str(Path(__file__).parent.parent / sqlite_path)
+# 确保数据目录存在
+Path(sqlite_path).parent.mkdir(parents=True, exist_ok=True)
 
-    engine = create_async_engine(
-        f"sqlite+aiosqlite:///{sqlite_path}",
-        echo=False,
-    )
-else:
-    # PostgreSQL 配置
-    engine = create_async_engine(
-        DB_URL,
-        echo=False,
-        poolclass=NullPool,
-        pool_pre_ping=True,
-    )
+engine = create_async_engine(
+    f"sqlite+aiosqlite:///{sqlite_path}",
+    echo=False,
+)
 
 # ──────────────────────────── 会话工厂 ────────────────────────────
 
@@ -61,47 +52,21 @@ async def get_db() -> AsyncGenerator[AsyncSession, None]:
     FastAPI 依赖项：获取异步数据库会话。
     """
     async with async_session_factory() as session:
-        try:
-            yield session
-            await session.commit()
-        except Exception:
-            await session.rollback()
-            raise
+        yield session
 
 
-# ──────────────────────────── 生命周期辅助 ────────────────────────────
+async def close_db() -> None:
+    """关闭数据库连接池"""
+    await engine.dispose()
+
 
 async def init_db() -> None:
     """初始化数据库：建表"""
     from app.models.base import Base
 
     async with engine.begin() as conn:
-        if IS_SQLITE:
-            # SQLite 启用 WAL 模式和外键约束
-            await conn.execute(text("PRAGMA journal_mode=WAL"))
-            await conn.execute(text("PRAGMA foreign_keys=ON"))
+        # SQLite 启用 WAL 模式和外键约束
+        await conn.execute(text("PRAGMA journal_mode=WAL"))
+        await conn.execute(text("PRAGMA foreign_keys=ON"))
         # 创建所有表
         await conn.run_sync(Base.metadata.create_all)
-
-    if not IS_SQLITE:
-        # PostgreSQL 需要创建扩展
-        async with engine.begin() as conn:
-            try:
-                await conn.execute(text("CREATE EXTENSION IF NOT EXISTS vector"))
-            except Exception:
-                pass
-            try:
-                await conn.execute(text("CREATE EXTENSION IF NOT EXISTS zhparser"))
-            except Exception:
-                pass
-            try:
-                await conn.execute(text(
-                    "CREATE TEXT SEARCH CONFIGURATION IF NOT EXISTS chinese_zh (PARSER = zhparser)"
-                ))
-            except Exception:
-                pass
-
-
-async def close_db() -> None:
-    """关闭数据库引擎"""
-    await engine.dispose()