fix: resolve CHANGELOG.md path issue for Docker deployment

- Update changelog.go to use binary directory as base path
  - Uses os.Executable() instead of relative path '..'
  - Automatically adapts to local and Docker environments

- Modify server Dockerfile build context
  - Change context from ./server to project root (.)
  - Update COPY commands for new context
  - Add CHANGELOG.md to container image

- Update AGENTS.md guidelines
  - Explicitly specify relative path format for file references

This ensures the changelog API works correctly in both local development
and Docker deployment environments.

server/service/changelog.go

@@ -20,8 +20,11 @@ func ParseChangelog() ([]ChangelogEntry, error) {
 	// 获取项目根目录
 	rootDir := os.Getenv("PROJECT_ROOT")
 	if rootDir == "" {
-		// 如果未设置，使用相对路径推测
-		rootDir = ".."
+		// 使用二进制文件所在目录作为基准
+		execPath, err := os.Executable()
+		if err == nil {
+			rootDir = filepath.Dir(execPath)
+		}
 	}
 
 	changelogPath := filepath.Join(rootDir, "CHANGELOG.md")