refactor(storage): move LocalProvider to internal/storage package

Move LocalProvider from cmd/bd/doctor/git.go to internal/storage/local_provider.go
where it belongs alongside StorageProvider. Both implement IssueProvider for
orphan detection - LocalProvider for direct SQLite access (--db flag),
StorageProvider for the global Storage interface.

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

cmd/bd/orphans.go

@@ -113,7 +113,7 @@ type orphanIssueOutput struct {
 func getIssueProvider() (types.IssueProvider, func(), error) {
 	// If --db flag is set and we have a dbPath, create a provider from that path
 	if dbPath != "" {
-		provider, err := doctor.NewLocalProvider(dbPath)
+		provider, err := storage.NewLocalProvider(dbPath)
 		if err != nil {
 			return nil, nil, fmt.Errorf("failed to open database at %s: %w", dbPath, err)
 		}