Update PLANNING.md §2 from empty checkboxes to the working answers in
decision-log, fix the reverse OS/self-app wording, and clarify roadmap
Phase 3 so OS-layer growth does not rewrite the start order.
Co-authored-by: okuma <o0kuma@users.noreply.github.com>
Resolves the open Q1-Q7 questions as tentative decisions (self-app beta
first, target consumers, MVP scenario = read-receipt relief + group-chat
catch-up, autonomy capped at L0-L2) and builds the standard deliverable
set on top of them, ready for review at the next meeting.