添加AI生成表头功能并重构前端状态管理

- 后端：实现AI生成表头逻辑，当模板为空或字段为自动生成时调用AI分析并生成合适字段
- 后端：添加_is_auto_generated_field方法识别自动生成的无效表头字段
- 后端：修改_get_template_fields_from_excel方法支持文件类型参数
- 前端：创建TemplateFillContext提供全局状态管理
- 前端：将TemplateFill页面状态迁移到Context中统一管理
- 前端：移除页面内重复的状态定义和方法实现

frontend/src/context/TemplateFillContext.tsx

@@ -0,0 +1,114 @@
+import React, { createContext, useContext, useState, ReactNode } from 'react';
+
+type SourceFile = {
+  file: File;
+  preview?: string;
+};
+
+type TemplateField = {
+  cell: string;
+  name: string;
+  field_type: string;
+  required: boolean;
+  hint?: string;
+};
+
+type Step = 'upload' | 'filling' | 'preview';
+
+interface TemplateFillState {
+  step: Step;
+  templateFile: File | null;
+  templateFields: TemplateField[];
+  sourceFiles: SourceFile[];
+  sourceFilePaths: string[];
+  templateId: string;
+  filledResult: any;
+  setStep: (step: Step) => void;
+  setTemplateFile: (file: File | null) => void;
+  setTemplateFields: (fields: TemplateField[]) => void;
+  setSourceFiles: (files: SourceFile[]) => void;
+  addSourceFiles: (files: SourceFile[]) => void;
+  removeSourceFile: (index: number) => void;
+  setSourceFilePaths: (paths: string[]) => void;
+  setTemplateId: (id: string) => void;
+  setFilledResult: (result: any) => void;
+  reset: () => void;
+}
+
+const initialState = {
+  step: 'upload' as Step,
+  templateFile: null,
+  templateFields: [],
+  sourceFiles: [],
+  sourceFilePaths: [],
+  templateId: '',
+  filledResult: null,
+  setStep: () => {},
+  setTemplateFile: () => {},
+  setTemplateFields: () => {},
+  setSourceFiles: () => {},
+  addSourceFiles: () => {},
+  removeSourceFile: () => {},
+  setSourceFilePaths: () => {},
+  setTemplateId: () => {},
+  setFilledResult: () => {},
+  reset: () => {},
+};
+
+const TemplateFillContext = createContext<TemplateFillState>(initialState);
+
+export const TemplateFillProvider: React.FC<{ children: ReactNode }> = ({ children }) => {
+  const [step, setStep] = useState<Step>('upload');
+  const [templateFile, setTemplateFile] = useState<File | null>(null);
+  const [templateFields, setTemplateFields] = useState<TemplateField[]>([]);
+  const [sourceFiles, setSourceFiles] = useState<SourceFile[]>([]);
+  const [sourceFilePaths, setSourceFilePaths] = useState<string[]>([]);
+  const [templateId, setTemplateId] = useState<string>('');
+  const [filledResult, setFilledResult] = useState<any>(null);
+
+  const addSourceFiles = (files: SourceFile[]) => {
+    setSourceFiles(prev => [...prev, ...files]);
+  };
+
+  const removeSourceFile = (index: number) => {
+    setSourceFiles(prev => prev.filter((_, i) => i !== index));
+  };
+
+  const reset = () => {
+    setStep('upload');
+    setTemplateFile(null);
+    setTemplateFields([]);
+    setSourceFiles([]);
+    setSourceFilePaths([]);
+    setTemplateId('');
+    setFilledResult(null);
+  };
+
+  return (
+    <TemplateFillContext.Provider
+      value={{
+        step,
+        templateFile,
+        templateFields,
+        sourceFiles,
+        sourceFilePaths,
+        templateId,
+        filledResult,
+        setStep,
+        setTemplateFile,
+        setTemplateFields,
+        setSourceFiles,
+        addSourceFiles,
+        removeSourceFile,
+        setSourceFilePaths,
+        setTemplateId,
+        setFilledResult,
+        reset,
+      }}
+    >
+      {children}
+    </TemplateFillContext.Provider>
+  );
+};
+
+export const useTemplateFill = () => useContext(TemplateFillContext);