Open M3 repo for M2.7 feedback collection

- README: announce M3, point users at M2.7 in the meantime, and explain
  how to send bugs / capability requests / benchmark gaps / deployment
  issues. Preserves the M2.7 brand header, community links, platform
  links, and contact email.
- Issue templates: bug report, capability request, benchmark gap,
  deployment issue. config.yml disables blank issues and surfaces
  WeChat / Discord / email as contact links.
- figures/: M2.7 logo assets so the README renders correctly.