docs(handoff): finalize M0-M6 delivery handoff and verification boundaries - #6

Summary

This PR finalizes the documentation, architectural alignment, requirement-to-evidence matrix, and delivery handoff for Berry AI Studio Milestones M0 through M6.

Key Content

• Product Architecture & Specifications:
  • \docs/PRODUCT_VISION.md: Vision and principles (simplicity over spaghetti nodes, 5-type contract, API-first).
  • \docs/PRD.md: Complete Product Requirements Document.
  • \docs/ARCHITECTURE.md: System architecture, runtime hierarchy, and rollback boundaries.
  • \docs/ROADMAP.md: Milestones 0 through 6 delivery roadmap and acceptance gates.
  • \docs/SUPPORT_MATRIX.md: Hardware, engine, and provider support boundaries.
  • \docs/LAUNCHER_MANAGER_REQUIREMENTS.md: Launcher and manager requirements (L01–L12).
  • \docs/USER_GUIDE.md: End-user walkthrough, CLI commands, and troubleshooting guide.
• Truthful Requirement Verification & Handoff:
  • \docs/RELEASE_VERIFICATION_REPORT.md: Detailed line-by-line verification report for R01–R18 and L01–L12.
  • \docs/DELIVERY_HANDOFF_M0_M6.md: Requirement-to-evidence matrix distinguishing automated test runs, Windows runs, local engines, cloud providers, and unverified scenarios.
  • Explicit documentation of update & rollback boundaries: source checkout vs. packaged Windows distribution; git rollback vs. virtualenv wheel non-reversion.
• Repository Documentation:
  • \README.md: Aligned overview with quickstart for both packaged users and developers.