docs: resolve all open ADR questions to their designed recommendations

The owner delegated the remaining calls ("follow what is designed"), so every
still-open OPEN-QUESTIONS entry is locked to its stated recommendation, with a
Decision line and the consuming milestone tagged. Covers the M0 calls already
embodied in the shipped spine (CLI-only/no daemon, Linux+WSL2 first, Docker-only),
the M4/M5 provider/proxy/CA choices, the M6 saga/health/hooks/profiles/doctor
policies, and the v2/later registry/telemetry/remote-backend defaults. Each is
revisitable at its milestone on concrete evidence only.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

Author: gustavobertoi