feat(internal/config): add TitleOverride in rust config (#3242)

Add `TitleOverride` in rust module so it can be correctly set to
codec.Source.

This field is missing when generating google-cloud-firestore.

Fixes #3199

Author: JoeWang1127

devtools/cmd/migrate-sidekick/main.go

@@ -502,6 +502,7 @@ func buildModules(path string) ([]*config.RustModule, error) {
 		includedIds, _ := sidekick.Source["included-ids"].(string)
 		includeList, _ := sidekick.Source["include-list"].(string)
 		skippedIds, _ := sidekick.Source["skipped-ids"].(string)
+		titleOverride, _ := sidekick.Source["title-override"].(string)
 
 		hasVeneer, _ := sidekick.Codec["has-veneer"].(string)
 		includeGrpcOnlyMethods, _ := sidekick.Codec["include-grpc-only-methods"].(string)
@@ -530,6 +531,7 @@ func buildModules(path string) ([]*config.RustModule, error) {
 			SkippedIds:             strToSlice(skippedIds),
 			Source:                 sidekick.General.SpecificationSource,
 			Template:               strings.TrimPrefix(templateOverride, "templates/"),
+			TitleOverride:          titleOverride,
 		})
 
 		return nil

devtools/cmd/migrate-sidekick/main_test.go

@@ -411,6 +411,7 @@ func TestBuildVeneer(t *testing.T) {
 								SkippedIds:             []string{".google.iam.v1.ResourcePolicyMember"},
 								Source:                 "google/storage/v2",
 								Template:               "grpc-client",
+								TitleOverride:          "Cloud Firestore API",
 							},
 							{
 								GenerateSetterSamples: false,

devtools/cmd/migrate-sidekick/testdata/build-veneer/success/lib-1/dir-1/.sidekick.toml

@@ -11,6 +11,7 @@ included-ids = """\
     .google.storage.v2.Storage.ListBuckets\
     """
 skipped-ids = ".google.iam.v1.ResourcePolicyMember"
+title-override = 'Cloud Firestore API'
 
 [codec]
 copyright-year            = '2025'

internal/config/language.go

@@ -87,6 +87,9 @@ type RustModule struct {
 	// Template specifies which generator template to use.
 	// Valid values: "grpc-client", "http-client", "prost", "convert-prost", "mod".
 	Template string `yaml:"template"`
+
+	// TitleOverride overrides the crate title.
+	TitleOverride string `yaml:"title_override,omitempty"`
 }
 
 // RustCrate contains Rust-specific library configuration.

internal/librarian/internal/rust/codec.go

@@ -214,6 +214,9 @@ func moduleToSidekickConfig(library *config.Library, module *config.RustModule,
 	if module.IncludeList != "" {
 		source["include-list"] = module.IncludeList
 	}
+	if module.TitleOverride != "" {
+		source["title-override"] = module.TitleOverride
+	}
 
 	language := "rust"
 	if module.Template == "prost" {