Datapack is saved into a dimension folder on 26.x, so it never loads on fresh servers #776

Describe the bug
On a fresh 26.x server, initializeDatapack() saves movecraft-data.zip into a dimension folder instead of the world's datapacks folder, so the server never loads it.

Since 26.x, World#getWorldFolder() returns the dimension folder (world/dimensions/minecraft/<dimension>), while datapacks are still read from world/datapacks. The loop in Movecraft#initializeDatapack() never checks world/datapacks (which already exists), falls through to the last world, and writes the pack to world/dimensions/minecraft/the_end/datapacks.

This is a different cause from #434: restarting does not fix it, and after a restart Movecraft looks enabled but loads no craft types.

To Reproduce

1. Start a fresh Paper 26.2 server with only Movecraft installed.
2. First start: the pack is written to world/dimensions/minecraft/the_end/datapacks, Failed to automatically load movecraft datapack is logged, and Movecraft disables itself with an IllegalPluginAccessException.
3. Restart: Conflicting datapack already exists in ./world/dimensions/minecraft/the_end/datapacks is logged and Movecraft enables, but the pack is still not loaded and /crafttype list is empty, so no craft can be piloted.

Expected behavior
The datapack is saved to world/datapacks, loaded and enabled on first start, and craft types load.

Workaround
Move movecraft-data.zip from world/dimensions/minecraft/the_end/datapacks to world/datapacks and restart. Movecraft then enables normally and loads the craft types.

Versions:

• Movecraft: 8.0.0_beta-6, dev build from main @ b49f891 (Actions run 42399290477)
• Addons: none
• Java: Eclipse Temurin 25.0.4.1
• Minecraft: Paper 26.2 build 135

Additional context
Also reproduced on Paper 26.3 build 248 with the build from #775. Existing servers are not affected if the pack was already installed in world/datapacks before upgrading to 26.x.

Possibly a separate issue: after initializeDatapack() calls setEnabled(false), onEnable() keeps going and schedules tasks, which causes the IllegalPluginAccessException.