meteor3: port all 18 migration up() bodies to async
percolate:migrations 2.0.1 awaits async up(), so historical migrations
now run on Meteor 3: fetchAsync + for..of instead of cursor forEach,
insert/update/remove -> *Async, _ensureIndex -> createIndexAsync,
Accounts.createUser -> createUserAsync, awaited rawCollection indexes.
Verified: empty Mongo 7 DB migrates 0->18 cleanly (indexes + industry
registries created, control unlocked at v18); pre-marking version=18 is
no longer needed (UPGRADE.md updated). REST smoke stays byte-identical.
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