Fix slayer assignment names and silent mausoleum gates

[HarleyGilpin]

Fixes two reported bugs.

Slayer assignment names showing underscores (#1153)

The enchanted gem and ring of slaying "Kills-left" option printed slayerTask.lowercase(), which is the raw variable key, so the message read "moss_giants". Uses toLowerSpaceCase() now, the same conversion the slayer master dialogue already applies.

While in there: the reassign/block panel of the slayer rewards interface read slayer_assignment, a key nothing writes, so both lines always showed "You must have an assignment to use this." even with a task active. It reads slayerTask now and formats with toSentenceCase(), matching the blocked task list above it.

No gate sound in the mausoleum (#1140)

Two problems, both silent.

The sound name never existed. Door.sound builds ${material}_${gate|door}_${suffix}, so the two gates below the mausoleum (objects 3444 and 3445, material = "grate", named "Gate") asked for grate_gate_open. Nothing defines that, and Character.sound returns silently on an unknown id.

Material names follow two conventions: some name the door type (iron_door_open, barrows_door_open), others name the sound itself (grate_open). The lookup falls back through ${material}_${type}_$suffix, ${material}_$suffix, then the generic ${type}_$suffix, so a material without a dedicated sound plays the plain door or gate sound instead of nothing. Only grate changes behaviour; iron and barrows already resolved on the first candidate.

Also adds the missing grate_close, sfx 68, next to the existing grate_open 67, and sets the material on the opened variants of both gates so closing matches opening.

Reverting a temporary object played nothing. Doors opened by enterDoor revert after a few ticks, and the 5 minute reset does the same for doors left open, so the gate was silent again the moment the player stepped past it.

GameObjects.replace and Replace.objects take an optional onRevert callback, invoked once the original objects are back. Door passes the opposite sound to whichever transition it made, as an area sound at the door tile so anyone nearby hears it rather than only the player who opened it. Threaded through DoubleDoor and Gate so double doors behave the same.

resetExisting fires that same timer early when a player manually closes a door that was going to reset on its own, so the explicit sound in that branch is dropped; the revert plays it now, and keeping both would play it twice.

Sfx ids verified against the rev 634 sound table (GRATE_CLOSE 68, GRATE_OPEN 69).

Testing

DoorSoundTest walks a player through the first mausoleum gate and asserts a grate_close zone sound lands once the gate reverts. Full ./gradlew test passes.

Closes #1153
Closes #1140