docs(readme): restructure for public-repo readability

[wahyuwidharto]

Summary

Restructuring pass on the README ahead of the repo going public. Every sentence survives — only headings, positions, and the intro feature bullets change. No behavior, code, or doc-of-record content touched.

• Table of contents added after the intro.
• Milestone paragraphs (M4 / M5.A / M5.B / M5.C) moved out of Quick start into a dedicated ## Feature deep-dives section — their bold leads become ### headings, prose verbatim. Quick start now ends cleanly at the smoke check.
• Golden flow promoted to its own ## Try the full flow H2 (was an H3 buried under Quick start).
• Admin-authorization blockquote promoted to an ### Admin authorization subsection under Architecture — same text, scannable and linkable.
• ## Status renamed to ## Documentation and the sources-of-truth table moved below the visitor-facing sections (Quick start → Architecture → Deploy → Game integration), keeping the v1.0.0 status line.
• "What's in the box" updated to match shipped scope — this is the one place existing prose is edited, please sanity-check:
  • "Two distribution models" → "Three distribution models" (adds ADT), and "One internal code pool and state machine for both" → "…for the two code-based models" since ADT ships a download URL, not a code.
  • New bullets for window enforcement, auto-approve, and the admin detail-page shell + announcements, each linking to its deep-dive.

Verification

• All TOC anchors + internal # links validated against generated GitHub heading anchors (script-checked).
• All relative file links verified to exist on disk.
• Docs-only change — no code, tests, or generated artifacts touched.

🤖 Generated with Claude Code