feat: 实现文件上传功能并完善测试覆盖

- 新增 upload.rs 模块，支持 multipart/form-data 文件上传
- 文件按日期存储在 storage/YYYY-MM-DD/ 目录下
- 使用 UUID 生成唯一文件名，保留原始扩展名
- 添加 axum-extra, uuid, chrono 依赖

新增测试用例:
- config_test.rs: 6 个测试 (配置结构验证)
- router_test.rs: 11 个测试 (路由匹配逻辑)
- handler_test.rs: 8 个测试 (请求处理)
- upload_test.rs: 13 个测试 (文件上传功能)

其他改进:
- 优化 handler.rs 代码注释
- 更新 .gitignore 忽略 storage/ 和 .claude/
- 添加 CLAUDE.md 项目指南文档

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

src/upload.rs

@@ -0,0 +1,150 @@
+use axum::{
+    body::Body,
+    extract::State,
+    http::StatusCode,
+    response::{IntoResponse, Response},
+};
+use axum_extra::extract::Multipart;
+use chrono::Local;
+use serde_json::json;
+use std::path::PathBuf;
+use std::sync::Arc;
+use tokio::fs;
+use uuid::Uuid;
+
+use crate::handler::AppState;
+
+/// 文件上传结果
+#[derive(Debug, serde::Serialize)]
+pub struct UploadResult {
+    pub success: bool,
+    pub files: Vec<FileInfo>,
+    pub message: String,
+}
+
+/// 单个文件信息
+#[derive(Debug, serde::Serialize)]
+pub struct FileInfo {
+    pub original_name: String,
+    pub stored_name: String,
+    pub path: String,
+    pub size: usize,
+    pub content_type: Option<String>,
+}
+
+impl UploadResult {
+    pub fn success(files: Vec<FileInfo>) -> Self {
+        UploadResult {
+            success: true,
+            files,
+            message: "Files uploaded successfully".to_string(),
+        }
+    }
+
+    pub fn error(message: String) -> Self {
+        UploadResult {
+            success: false,
+            files: vec![],
+            message,
+        }
+    }
+}
+
+impl IntoResponse for UploadResult {
+    fn into_response(self) -> Response {
+        let status = if self.success {
+            StatusCode::OK
+        } else {
+            StatusCode::BAD_REQUEST
+        };
+
+        let body = serde_json::to_string(&self).unwrap_or_else(|_| {
+            json!({
+                "success": false,
+                "files": [],
+                "message": "Failed to serialize response"
+            })
+            .to_string()
+        });
+
+        Response::builder()
+            .status(status)
+            .header("content-type", "application/json")
+            .body(Body::from(body))
+            .unwrap()
+    }
+}
+
+/// 处理文件上传
+pub async fn upload_handler(
+    State(_state): State<Arc<AppState>>,
+    mut multipart: Multipart,
+) -> impl IntoResponse {
+    let mut uploaded_files = Vec::new();
+
+    // 确保 storage 目录存在
+    let storage_root = PathBuf::from("storage");
+    if let Err(e) = fs::create_dir_all(&storage_root).await {
+        return UploadResult::error(format!("Failed to create storage directory: {}", e));
+    }
+
+    // 创建按日期分类的子目录
+    let date_dir = Local::now().format("%Y-%m-%d").to_string();
+    let upload_dir = storage_root.join(&date_dir);
+    if let Err(e) = fs::create_dir_all(&upload_dir).await {
+        return UploadResult::error(format!("Failed to create upload directory: {}", e));
+    }
+
+    // 处理每个上传的字段
+    while let Some(field) = multipart.next_field().await.unwrap_or(None) {
+        // 获取文件名
+        let original_name = field
+            .file_name()
+            .map(|s| s.to_string())
+            .unwrap_or_else(|| "unknown".to_string());
+
+        // 获取内容类型
+        let content_type = field.content_type().map(|s| s.to_string());
+
+        // 读取文件数据
+        let data = match field.bytes().await {
+            Ok(d) => d,
+            Err(e) => {
+                eprintln!("Failed to read file data: {}", e);
+                continue;
+            }
+        };
+
+        // 生成唯一文件名，保留原始扩展名
+        let extension = std::path::Path::new(&original_name)
+            .extension()
+            .and_then(|s| s.to_str())
+            .map(|s| format!(".{}", s))
+            .unwrap_or_default();
+
+        let stored_name = format!("{}{}", Uuid::new_v4(), extension);
+        let file_path = upload_dir.join(&stored_name);
+
+        // 保存文件
+        match fs::write(&file_path, &data).await {
+            Ok(_) => {
+                uploaded_files.push(FileInfo {
+                    original_name: original_name.clone(),
+                    stored_name: stored_name.clone(),
+                    path: format!("storage/{}/{}", date_dir, stored_name),
+                    size: data.len(),
+                    content_type,
+                });
+            }
+            Err(e) => {
+                eprintln!("Failed to save file {}: {}", original_name, e);
+            }
+        }
+    }
+
+    if uploaded_files.is_empty() {
+        UploadResult::error("No files were uploaded".to_string())
+    } else {
+        UploadResult::success(uploaded_files)
+    }
+}