RV/Boat Lots: sync lots to public rental_calendar amenities

Add a "Sync to Public Page" button that creates/updates one rental_calendar
amenity per lot (name, size · rate · availability in the description, rate in
booking_config, shown on the public page). Idempotent via amenities.source_rv_lot_id;
removes synced amenities for deleted lots.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

supabase/migrations/20260608001000_amenities_source_rv_lot_id.sql

@@ -0,0 +1,4 @@
+-- Link a synced public amenity back to its RV/Boat lot so re-syncing updates
+-- (rather than duplicates) the per-lot rental_calendar amenity.
+alter table public.amenities add column if not exists source_rv_lot_id uuid;
+create index if not exists idx_amenities_source_rv_lot_id on public.amenities(source_rv_lot_id);