docs: deduplicate install/troubleshooting across README and guides

Move one-liner install commands into GUIDE_INSTALL.md, replace README
install section with link table to guide. Remove duplicate troubleshooting
table from install guide (single source: GUIDE_TROUBLESHOOTING.md).
Add device testing guide + issue reporting links to all install sections.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>