fix(packages): accept npm "repository" and "bin" in string form (#38236)

## What

npm allows `repository` and `bin` in `package.json` to be either an
object or a plain string (npm docs:
[repository](https://docs.npmjs.com/cli/v11/configuring-npm/package-json#repository),
[bin](https://docs.npmjs.com/cli/v11/configuring-npm/package-json#bin)).
The npm registry creator modeled `repository` as a struct and `bin` as
`map[string]string`, so publishing a package whose `package.json` uses
the string form failed with:

```
json: cannot unmarshal string into Go struct field PackageMetadataVersion.PackageMetadata.versions.bin of type map[string]string
```

## Fix

`modules/packages/npm/creator.go`: add `UnmarshalJSON` to `Repository`
(string → `URL`) and a `Bin` type with `UnmarshalJSON` (string → a
single command named after the package, per npm semantics), mirroring
the existing `License` / `User` string-or-object handling. The stored
`Metadata` field types are unchanged.

`bundledDependencies` as a boolean (also noted in #38235) is left out of
scope — it is rare and semantically different (`true` = bundle all
deps).

## Test

`TestParsePackage/ValidRepositoryAndBinAsString` parses a package with
string `repository` and `bin`: it fails on `main` with the error above
and passes with this change. The full `modules/packages/npm` suite is
green and `gofmt` is clean.

Fixes #38235

_AI disclosure: prepared with AI assistance; I reviewed and verified it
(reproduction + tests) and can explain and defend the change._

modules/packages/npm/creator.go

@@ -103,7 +103,7 @@ type PackageMetadataVersion struct {
 	DevDependencies      map[string]string   `json:"devDependencies,omitempty"`
 	PeerDependencies     map[string]string   `json:"peerDependencies,omitempty"`
 	PeerDependenciesMeta map[string]any      `json:"peerDependenciesMeta,omitempty"`
-	Bin                  map[string]string   `json:"bin,omitempty"`
+	Bin                  Bin                 `json:"bin,omitempty"`
 	OptionalDependencies map[string]string   `json:"optionalDependencies,omitempty"`
 	Readme               string              `json:"readme,omitempty"`
 	Dist                 PackageDistribution `json:"dist"`
@@ -188,6 +188,49 @@ type Repository struct {
 	Directory string `json:"directory,omitempty"`
 }
 
+// UnmarshalJSON is needed because the repository field can be a string or an object.
+func (r *Repository) UnmarshalJSON(data []byte) error {
+	switch data[0] {
+	case '"':
+		var value string
+		if err := json.Unmarshal(data, &value); err != nil {
+			return err
+		}
+		r.URL = value
+	case '{':
+		type repositoryAlias Repository // avoid recursion into this method
+		var value repositoryAlias
+		if err := json.Unmarshal(data, &value); err != nil {
+			return err
+		}
+		*r = Repository(value)
+	}
+	return nil
+}
+
+// Bin maps command names to executable files. npm also allows a single string,
+// in which case the command is named after the package (resolved in ParsePackage).
+type Bin map[string]string
+
+// UnmarshalJSON is needed because the bin field can be a string or an object.
+func (b *Bin) UnmarshalJSON(data []byte) error {
+	switch data[0] {
+	case '"':
+		var value string
+		if err := json.Unmarshal(data, &value); err != nil {
+			return err
+		}
+		*b = Bin{"": value}
+	case '{':
+		var value map[string]string
+		if err := json.Unmarshal(data, &value); err != nil {
+			return err
+		}
+		*b = value
+	}
+	return nil
+}
+
 // PackageAttachment https://github.com/npm/registry/blob/master/docs/REGISTRY-API.md#package
 type PackageAttachment struct {
 	ContentType string `json:"content_type"`
@@ -229,6 +272,11 @@ func ParsePackage(r io.Reader) (*Package, error) {
 			meta.Homepage = ""
 		}
 
+		// A string "bin" means a single executable named after the package.
+		if cmd, ok := meta.Bin[""]; ok && len(meta.Bin) == 1 {
+			meta.Bin = Bin{name: cmd}
+		}
+
 		p := &Package{
 			Name:     meta.Name,
 			Version:  v.String(),

modules/packages/npm/creator_test.go

@@ -326,4 +326,31 @@ func TestParsePackage(t *testing.T) {
 		require.NoError(t, err)
 		require.Equal(t, "MIT", string(p.Metadata.License))
 	})
+
+	t.Run("ValidRepositoryAndBinAsString", func(t *testing.T) {
+		// npm allows "repository" and "bin" to be plain strings, not only objects.
+		packageJSON := `{
+  "versions": {
+		"0.1.1": {
+			"name": "dev-null",
+			"version": "0.1.1",
+			"bin": "./cli.js",
+			"repository": "https://gitea.io/gitea/test.git",
+			"dist": {
+				"integrity": "sha256-"
+			}
+		}
+	},
+	"_attachments": {
+		"foo": {
+			"data": "AAAA"
+		}
+	}
+}`
+		p, err := ParsePackage(strings.NewReader(packageJSON))
+		require.NoError(t, err)
+		require.Equal(t, "https://gitea.io/gitea/test.git", p.Metadata.Repository.URL)
+		// a string bin is named after the package
+		require.Equal(t, "./cli.js", p.Metadata.Bin["dev-null"])
+	})
 }