f9f451e0d6
Add ProgressiveFileReader state machine (Sampling/Ready/Error) with scanned_newlines cache for O(1) line lookups. Implement spawn_indexer() for background mmap-based indexing with cancellation and progress reporting. Add VisualHeightIndex with prefix-sum + binary search for O(log N) visual height queries. Register all new io submodules and extend FileReader with reload(), save_cache(), and accessor methods. Ultraworked with [Sisyphus](https://github.com/code-yeongyu/oh-my-openagent) Co-authored-by: Sisyphus <clio-agent@sisyphuslabs.ai>