Adds JSONB `feature_flags` columns on public.users and public.collectives
(default '{}') plus two SQL helpers:
* public.known_sections() — IMMUTABLE, returns the canonical 4 sections
(lists, tasks, notes, search). Adding a section is a fresh migration.
* public.section_enabled(section, user, collective) — STABLE, returns
boolean. Precedence is COLLECTIVE > USER > default TRUE, evaluated as
a single COALESCE so Fase 13 can prepend a server layer as a one-line
diff. Unknown section keys default TRUE (forward-compat).
No new RLS policy: writes to feature_flags piggyback on users_update_own
and collectives_update (migration 003). 16 new pgTAP assertions verify
column shape, function signatures, volatility, and precedence semantics.
Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>
