feat: 平台规则从硬编码改为品牌方上传文档 + AI 解析

- 新增 PlatformRule 模型 (draft/active/inactive 状态流转)
- 新增文档解析服务 (PDF/Word/Excel → 纯文本)
- 新增 4 个 API: 解析/确认/查询/删除平台规则
- 脚本审核优先从 DB 读取 active 规则，硬编码兜底
- 视频审核合并平台规则违禁词到检测列表
- Alembic 迁移 006: platform_rules 表

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

backend/app/services/document_parser.py

@@ -0,0 +1,119 @@
+"""
+文档解析服务
+从 PDF/Word/Excel 文档中提取纯文本
+"""
+import os
+import tempfile
+from typing import Optional
+
+import httpx
+
+
+class DocumentParser:
+    """从文档中提取纯文本"""
+
+    @staticmethod
+    async def download_and_parse(document_url: str, document_name: str) -> str:
+        """
+        下载文档并解析为纯文本
+
+        Args:
+            document_url: 文档 URL (TOS)
+            document_name: 原始文件名（用于判断格式）
+
+        Returns:
+            提取的纯文本
+        """
+        # 下载到临时文件
+        tmp_path: Optional[str] = None
+        try:
+            async with httpx.AsyncClient(timeout=60.0) as client:
+                resp = await client.get(document_url)
+                resp.raise_for_status()
+
+            ext = document_name.rsplit(".", 1)[-1].lower() if "." in document_name else ""
+            with tempfile.NamedTemporaryFile(delete=False, suffix=f".{ext}") as tmp:
+                tmp.write(resp.content)
+                tmp_path = tmp.name
+
+            return DocumentParser.parse_file(tmp_path, document_name)
+        finally:
+            if tmp_path and os.path.exists(tmp_path):
+                os.unlink(tmp_path)
+
+    @staticmethod
+    def parse_file(file_path: str, file_name: str) -> str:
+        """
+        根据扩展名选择解析器，返回纯文本
+
+        Args:
+            file_path: 本地文件路径
+            file_name: 原始文件名
+
+        Returns:
+            提取的纯文本
+        """
+        ext = file_name.rsplit(".", 1)[-1].lower() if "." in file_name else ""
+
+        if ext == "pdf":
+            return DocumentParser._parse_pdf(file_path)
+        elif ext in ("doc", "docx"):
+            return DocumentParser._parse_docx(file_path)
+        elif ext in ("xls", "xlsx"):
+            return DocumentParser._parse_xlsx(file_path)
+        elif ext == "txt":
+            return DocumentParser._parse_txt(file_path)
+        else:
+            raise ValueError(f"不支持的文件格式: {ext}")
+
+    @staticmethod
+    def _parse_pdf(path: str) -> str:
+        """pdfplumber 提取 PDF 文本"""
+        import pdfplumber
+
+        texts = []
+        with pdfplumber.open(path) as pdf:
+            for page in pdf.pages:
+                text = page.extract_text()
+                if text:
+                    texts.append(text)
+        return "\n".join(texts)
+
+    @staticmethod
+    def _parse_docx(path: str) -> str:
+        """python-docx 提取 Word 文本"""
+        from docx import Document
+
+        doc = Document(path)
+        texts = []
+        for para in doc.paragraphs:
+            if para.text.strip():
+                texts.append(para.text)
+        # 也提取表格内容
+        for table in doc.tables:
+            for row in table.rows:
+                row_text = "\t".join(cell.text.strip() for cell in row.cells if cell.text.strip())
+                if row_text:
+                    texts.append(row_text)
+        return "\n".join(texts)
+
+    @staticmethod
+    def _parse_xlsx(path: str) -> str:
+        """openpyxl 提取 Excel 文本（所有 sheet 拼接）"""
+        from openpyxl import load_workbook
+
+        wb = load_workbook(path, read_only=True, data_only=True)
+        texts = []
+        for sheet in wb.worksheets:
+            for row in sheet.iter_rows(values_only=True):
+                row_text = "\t".join(str(cell) for cell in row if cell is not None)
+                if row_text.strip():
+                    texts.append(row_text)
+        wb.close()
+        return "\n".join(texts)
+
+    @staticmethod
+    def _parse_txt(path: str) -> str:
+        """纯文本文件"""
+        with open(path, "r", encoding="utf-8") as f:
+            return f.read()