Chain places

Chain / brand store locations from All The Places (CC0). Ships CONFIG-GATED OFF: which brands to surface is an open founder decision, so the curated brand list (src/lib/sources/megalayers/vector/atp-places.ts ATP_BRANDS) is EMPTY by default and the layer is a graceful no-op until brands are curated. When enabled: one bounded static GeoJSON fetch per brand, client-direct, no key, no server, no tiler. Verify the live output host before enabling any brand.