feat(biji-houdaun): 实现用户注册、登录、 Markdown 文件和图片上传功能

- 新增用户注册、登录接口及服务实现
- 添加 Markdown 文件创建、更新接口及服务实现
- 实现图片上传、获取接口及服务实现
- 集成 Snowflake ID 生成器
- 添加全局异常处理和统一返回结果封装
- 配置跨域访问和静态资源处理
- 实现基础的 XSS 防护

biji-houdaun/src/main/java/com/test/bijihoudaun/controller/MarkdownController.java

@@ -0,0 +1,41 @@
+package com.test.bijihoudaun.controller;
+
+import com.test.bijihoudaun.entity.MarkdownFile;
+import com.test.bijihoudaun.service.MarkdownFileService;
+import org.springframework.beans.factory.annotation.Autowired;
+import org.springframework.http.ResponseEntity;
+import org.springframework.web.bind.annotation.*;
+
+@RestController
+@RequestMapping("/api/markdown")
+public class MarkdownController {
+
+    @Autowired
+    private MarkdownFileService markdownFileService;
+
+    @PostMapping
+    public ResponseEntity<MarkdownFile> createMarkdown(
+            @RequestParam Integer userId,
+            @RequestParam String title,
+            @RequestParam String fileName,
+            @RequestBody String content) {
+
+        MarkdownFile file = markdownFileService.createMarkdownFile(
+                userId, title, fileName, content);
+
+        return ResponseEntity.ok(file);
+    }
+
+    @PutMapping("/{id}")
+    public ResponseEntity<MarkdownFile> updateMarkdown(
+            @PathVariable Integer id,
+            @RequestBody String content) {
+
+        MarkdownFile file = markdownFileService.updateMarkdownContent(id, content);
+
+        if (file != null) {
+            return ResponseEntity.ok(file);
+        }
+        return ResponseEntity.notFound().build();
+    }
+}