📄[Docs] Reorganize project documentation - #61

Summary

• reduce the root README from 427 lines to a concise 79-line project entry point
• add a central docs index and focused architecture, privacy, dependency, and tool-status sources of truth
• preserve historical v1/v2 QA, UX, i18n, and Image Metadata privacy evidence
• update the v2 QA record for completed main promotion and v2.0.0-rc.1 pre-release publication
• remove the unreferenced one-line README.original.md placeholder

Validation

• git diff --check
• node tests/run-all.mjs
• focused repository-relative Markdown link check (64 links across 12 files)
• no active READY EXCEPT MANUAL QA, secure-metadata v0.1.0, or local Windows path references