Payouts were computed at completion from LIVE config, so an admin changing
multipliers mid-game would change the payout of an already-in-progress game.
- Migration 016 adds payout_escape_amount/payout_treasure_amount (BIGINT) and
the corresponding multipliers to the games table.
- Both game-start paths stamp the resolved payout amounts (computed from the
config in effect at entry) onto the game row.
- completeGame pays from the snapshot, falling back to live calculation only
for legacy games that predate the snapshot columns.
Adds payoutSnapshot.test.js proving a mid-game config change cannot alter an
in-flight payout. Full suite: 15 suites / 131 tests.