Adds the design doc, the first phase 1 plan, and the OrgCore package:
SourceText: UTF-8 with or without BOM; invalid input is read-only and re-encodes to its original bytes.- Lossless green/red syntax tree with UTF-16 lengths.
- Line classifier, element-aware TODO/priority settings scan, and a block-level parser (sections, headings, planning, drawers, blocks, keywords, tables, lists, footnotes, comments, fixed width).
- Tests: 44 unit, fuzz (2,000 seeded documents) and encoding cases; opt-in corpus test via
ORGSTAR_CORPUS.