Added explicit native-text semantic types and attributed-string keys for block kinds, pagination hints, and attachment placement.
Extended chapter preprocessing to inject semantic markers for WXRead-style hints such as avoidPageBreakInside, pageBreakBefore, pageBreakAfter, pageRelate, and image/body block semantics.
Renderer post-processing now strips those markers and applies real attributes before fragment-offset extraction, so semantic metadata is preserved without breaking the existing offset contract.
Verification
build_sim for ReadViewDemo on iOS Simulator succeeded on 2026-05-22.
