Bug Fixes

• Fix tokenizer panic on Unicode-heavy markdown files (#18): Added Unicode sanitization for box drawing, block elements, geometric shapes, and braille characters before tokenization. Added panic recovery to all Tokenizer methods as defense-in-depth against sugarme/tokenizer v0.3.0 bugs.
• Fix startup hang on macOS Apple Silicon (#17): Changed CoreML MLComputeUnits from ALL to CPU_AND_GPU to avoid Neural Engine compilation hangs. Added timeout-based session creation (60s for CoreML, 30s for CPU) with automatic CPU fallback when CoreML fails or times out.