Fix preview roll chances ignoring permission-locked rewards

[GenOpenDiesel]

Problem

Roll chances shown in the crate preview are always computed against the global reward pool (getRollChance() sums weights over crate.getRewards(rarity), ignoring the viewer).

However, the actual roll excludes rewards a player cannot win — Crate.rollReward(player, rarity) builds its pool from getRewards(player, rarity), which filters by canWin(player) (permissions/requirements), at both the rarity and the reward level.

Result: a player without permission to a gated reward sees that reward hidden in the preview (Hide_Unavailable), while every remaining reward still shows its global percentage. Those percentages no longer sum to 100% and understate the player's real odds, so the preview looks broken.

Fix

Add a player-aware getRollChance(@Nullable Player player) that derives the chance from the pool actually available to that player:

• Crate#getRarities(@Nullable Player) — rarities reachable by the player.
• Rarity#getRollChance(Crate, @Nullable Player) — rarity chance over the player's reachable rarities.
• AbstractReward#getRollChance(Player) — within-rarity weight over the player's winnable rewards; returns 0% for a reward the player cannot win.
• PreviewMenu now fills %reward_roll_chance% / %reward_rarity_roll_chance% using the viewer.

The existing no-arg getRollChance() simply delegates to getRollChance(null) (the global pool), so editor/admin displays and any other callers are unchanged.

Behaviour after the fix

• Player without permission: locked reward stays hidden, remaining rewards show their real odds and sum to 100%.
• Player with permission: unchanged.
• With Hide_Unavailable: false: a locked reward shows 0% alongside the existing "no access" lore.

Notes

Compile not run locally (no Maven configured on this machine); changes are additive and were reviewed by hand. The change is behaviorally scoped to the preview — rolling logic is untouched.