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

internal/storage/local_test.go

@@ -0,0 +1,130 @@
+package storage
+
+import (
+	"context"
+	"io"
+	"os"
+	"strings"
+	"testing"
+)
+
+func TestSaveAndOpen(t *testing.T) {
+	dir := t.TempDir()
+	store, err := NewLocalStorage(dir)
+	if err != nil {
+		t.Fatalf("NewLocalStorage: %v", err)
+	}
+	ctx := context.Background()
+
+	content := "hello, mygo storage"
+	written, err := store.Save(ctx, "test/hello.txt", strings.NewReader(content))
+	if err != nil {
+		t.Fatalf("Save: %v", err)
+	}
+	if written != int64(len(content)) {
+		t.Errorf("written = %d, want %d", written, len(content))
+	}
+
+	reader, err := store.Open(ctx, "test/hello.txt")
+	if err != nil {
+		t.Fatalf("Open: %v", err)
+	}
+	defer reader.Close()
+
+	got, err := io.ReadAll(reader)
+	if err != nil {
+		t.Fatalf("ReadAll: %v", err)
+	}
+	if string(got) != content {
+		t.Errorf("content = %q, want %q", string(got), content)
+	}
+
+	// Verify the file exists on disk under the base path.
+	expectedPath := dir + "/test/hello.txt"
+	if _, err := os.Stat(expectedPath); err != nil {
+		t.Errorf("file not found on disk at %s: %v", expectedPath, err)
+	}
+}
+
+func TestDelete(t *testing.T) {
+	dir := t.TempDir()
+	store, err := NewLocalStorage(dir)
+	if err != nil {
+		t.Fatalf("NewLocalStorage: %v", err)
+	}
+	ctx := context.Background()
+
+	_, err = store.Save(ctx, "to_delete.txt", strings.NewReader("delete me"))
+	if err != nil {
+		t.Fatalf("Save: %v", err)
+	}
+
+	if err := store.Delete(ctx, "to_delete.txt"); err != nil {
+		t.Fatalf("Delete: %v", err)
+	}
+
+	_, err = store.Open(ctx, "to_delete.txt")
+	if err == nil {
+		t.Error("Open should fail after delete")
+	}
+}
+
+func TestDeleteIdempotent(t *testing.T) {
+	dir := t.TempDir()
+	store, err := NewLocalStorage(dir)
+	if err != nil {
+		t.Fatalf("NewLocalStorage: %v", err)
+	}
+	ctx := context.Background()
+
+	// Deleting a non-existent file should not error.
+	if err := store.Delete(ctx, "nonexistent.txt"); err != nil {
+		t.Errorf("Delete nonexistent should be idempotent, got: %v", err)
+	}
+}
+
+func TestPathTraversalRejected(t *testing.T) {
+	dir := t.TempDir()
+	store, err := NewLocalStorage(dir)
+	if err != nil {
+		t.Fatalf("NewLocalStorage: %v", err)
+	}
+	ctx := context.Background()
+
+	_, err = store.Save(ctx, "../escape.txt", strings.NewReader("malicious"))
+	if err == nil {
+		t.Error("Save should reject path traversal")
+	} else if !strings.Contains(err.Error(), "path traversal") {
+		t.Errorf("expected path traversal error, got: %v", err)
+	}
+
+	_, err = store.Open(ctx, "../escape.txt")
+	if err == nil {
+		t.Error("Open should reject path traversal")
+	} else if !strings.Contains(err.Error(), "path traversal") {
+		t.Errorf("expected path traversal error, got: %v", err)
+	}
+
+	err = store.Delete(ctx, "../escape.txt")
+	if err == nil {
+		t.Error("Delete should reject path traversal")
+	} else if !strings.Contains(err.Error(), "path traversal") {
+		t.Errorf("expected path traversal error, got: %v", err)
+	}
+}
+
+func TestOpenMissingFile(t *testing.T) {
+	dir := t.TempDir()
+	store, err := NewLocalStorage(dir)
+	if err != nil {
+		t.Fatalf("NewLocalStorage: %v", err)
+	}
+	ctx := context.Background()
+
+	_, err = store.Open(ctx, "no/such/file.txt")
+	if err == nil {
+		t.Error("Open should error for missing file")
+	} else if !strings.Contains(err.Error(), "not found on disk") {
+		t.Errorf("expected 'not found on disk' error, got: %v", err)
+	}
+}