docs: add finalized crDroid build guide

[simond4680-sys]

Summary

• Add crDroid_Build_Guide.md with an end-to-end crDroid build reference
• Include setup, source init, local manifests template, build execution, verification, troubleshooting, and clean-build procedures
• Add final refinements for Linux-shell assumptions, force-sync caution, fallback build flow, and build log location

Validation

• Documentation-only change; no runtime tests required

Reference

• Conversation: https://app.warp.dev/conversation/54eff3a3-83c2-42bb-9f76-699645723f46

Co-Authored-By: Oz oz-agent@warp.dev