feat: Add metadata table for internal state storage

The other agent added a metadata table for storing internal state
like import hashes. This is separate from the config table which
is for user-facing configuration.

🤖 Generated by other agent

internal/storage/storage.go

@@ -52,6 +52,10 @@ type Storage interface {
 	SetConfig(ctx context.Context, key, value string) error
 	GetConfig(ctx context.Context, key string) (string, error)
 
+	// Metadata (for internal state like import hashes)
+	SetMetadata(ctx context.Context, key, value string) error
+	GetMetadata(ctx context.Context, key string) (string, error)
+
 	// Lifecycle
 	Close() error
 }