fix: 添加 PyMuPDF 详细错误信息并创建缺失的迁移文件

- extraction.py: 添加更详细的 ImportError 错误信息，显示具体原因
- migrate_016.py: 创建 insurance_ppt_sessions 表（修复 500 错误）

解决 PDF 上传失败问题：
1. PyMuPDF 导入失败时显示具体错误原因
2. 数据库表 insurance_ppt_sessions 不存在导致插入失败

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

api/insurance/db/migrate_016.py

@@ -0,0 +1,55 @@
+"""迁移 016: 创建 insurance_ppt_sessions 表。"""
+import logging
+
+logger = logging.getLogger(__name__)
+
+
+def migrate():
+    """迁移入口。"""
+    from insurance.db.compat import db
+    from sqlalchemy import text
+
+    dialect = db.engine.dialect.name
+    is_postgres = dialect == 'postgresql'
+
+    if is_postgres:
+        sql = """
+            CREATE TABLE IF NOT EXISTS insurance_ppt_sessions (
+                id VARCHAR(36) PRIMARY KEY,
+                user_id VARCHAR(64) NOT NULL,
+                status VARCHAR(20) DEFAULT 'created' NOT NULL,
+                files_json TEXT,
+                extractions_json TEXT,
+                chat_history_json TEXT,
+                ppt_path VARCHAR(500),
+                markdown_path VARCHAR(500),
+                preview_paths_json TEXT,
+                preview_pdf_path VARCHAR(500),
+                slide_count INTEGER,
+                created_at TIMESTAMP DEFAULT NOW(),
+                updated_at TIMESTAMP DEFAULT NOW()
+            )
+        """
+    else:
+        sql = """
+            CREATE TABLE IF NOT EXISTS insurance_ppt_sessions (
+                id VARCHAR(36) PRIMARY KEY,
+                user_id VARCHAR(64) NOT NULL,
+                status VARCHAR(20) DEFAULT 'created' NOT NULL,
+                files_json TEXT,
+                extractions_json TEXT,
+                chat_history_json TEXT,
+                ppt_path VARCHAR(500),
+                markdown_path VARCHAR(500),
+                preview_paths_json TEXT,
+                preview_pdf_path VARCHAR(500),
+                slide_count INTEGER,
+                created_at TIMESTAMP DEFAULT CURRENT_TIMESTAMP,
+                updated_at TIMESTAMP DEFAULT CURRENT_TIMESTAMP
+            )
+        """
+
+    logger.info("[migrate_016] 创建 insurance_ppt_sessions 表 ...")
+    db.session.execute(text(sql))
+    db.session.commit()
+    logger.info("[migrate_016] insurance_ppt_sessions 表创建完成")

api/insurance/ppt/extraction.py

@@ -98,8 +98,11 @@ def _extract_pdf_text(pdf_path: str, max_chars: int = 30000) -> str:
         if len(full_text) > max_chars:
             full_text = full_text[:max_chars]
         return full_text
-    except ImportError:
-        logger.warning("PyMuPDF 未安装，无法提取 PDF 文本")
+    except ImportError as e:
+        logger.warning(f"PyMuPDF 未安装，无法提取 PDF 文本: {e}")
+        return ""
+    except Exception as e:
+        logger.warning(f"PyMuPDF 导入异常: {e}")
         return ""