## Summary
Converts `RewardGump` and the inner `RewardConfirmGump` from legacy `Gump` to `DynamicGump` with the static `DisplayTo` entry-point pattern.
Both gumps have variable per-instance layout — the reward grid loops over `_rewards` and adds `AddItem(itemID, hue)` / `AddTooltip(tooltipID)` calls whose values are baked into the layout buffer per entry, so a cached static layout would be incorrect. DynamicGump is the right choice and avoids the placeholder dance for non-text values.
Constructors are private; `DisplayTo` validates `NetState`, null `rewards`/`onPicked`, and empty arrays before constructing.
Builder labels use `$"{value}"` interpolated-string-handler form for zero-allocation text.
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