Add file management API with local storage backend

- Implement FileHandler with CRUD operations for files/directories
- Add FileService with business logic and SHA-256 hashing
- Create LocalStorage backend for filesystem persistence
- Add database repository with pagination and name uniqueness
  constraints
- Configure max upload size in storage settings
- Include comprehensive tests for all layers

go.mod

@@ -3,6 +3,7 @@ module github.com/dhao2001/mygo
 go 1.26.2
 
 require (
+	github.com/gabriel-vasile/mimetype v1.4.12
 	github.com/gin-gonic/gin v1.12.0
 	github.com/golang-jwt/jwt/v5 v5.3.1
 	github.com/google/uuid v1.6.0
@@ -20,7 +21,6 @@ require (
 	github.com/bytedance/sonic/loader v0.5.0 // indirect
 	github.com/cloudwego/base64x v0.1.6 // indirect
 	github.com/fsnotify/fsnotify v1.9.0 // indirect
-	github.com/gabriel-vasile/mimetype v1.4.12 // indirect
 	github.com/gin-contrib/sse v1.1.0 // indirect
 	github.com/go-playground/locales v0.14.1 // indirect
 	github.com/go-playground/universal-translator v0.18.1 // indirect