feat(files): add folder download as zip

- Add zip folder API endpoint
- Add download button to folder rows
- Enforce max archive size limit
- Document endpoint in OpenAPI

lib/files/zip_test.go

@@ -0,0 +1,60 @@
+package files
+
+import (
+	"archive/zip"
+	"io"
+	"os"
+	"path/filepath"
+	"testing"
+)
+
+func TestZipDirectory(t *testing.T) {
+	t.Parallel()
+	root := t.TempDir()
+	sub := filepath.Join(root, "nested")
+	if err := os.Mkdir(sub, 0o755); err != nil {
+		t.Fatal(err)
+	}
+	if err := os.WriteFile(filepath.Join(root, "a.txt"), []byte("hello"), 0o644); err != nil {
+		t.Fatal(err)
+	}
+	if err := os.WriteFile(filepath.Join(sub, "b.txt"), []byte("world"), 0o644); err != nil {
+		t.Fatal(err)
+	}
+
+	zipPath, err := ZipDirectory(root, 1<<20)
+	if err != nil {
+		t.Fatal(err)
+	}
+	defer os.Remove(zipPath)
+
+	r, err := zip.OpenReader(zipPath)
+	if err != nil {
+		t.Fatal(err)
+	}
+	defer r.Close()
+	names := make(map[string]string)
+	for _, f := range r.File {
+		rc, err := f.Open()
+		if err != nil {
+			t.Fatal(err)
+		}
+		body, err := io.ReadAll(rc)
+		_ = rc.Close()
+		if err != nil {
+			t.Fatal(err)
+		}
+		names[f.Name] = string(body)
+	}
+	if names["a.txt"] != "hello" || names["nested/b.txt"] != "world" {
+		t.Fatalf("unexpected zip contents: %#v", names)
+	}
+}
+
+func TestZipArchiveName(t *testing.T) {
+	t.Parallel()
+	dir := filepath.Join("Users", "dan", "Projects")
+	if got := ZipArchiveName(dir); got != "Projects.zip" {
+		t.Fatalf("ZipArchiveName() = %q", got)
+	}
+}