Fix Ender Dragon damage, End portal transition, and End Poem crash

[itsRevela]

Description

• Fixes three End dimension issues on dedicated servers: Ender Dragon immune to melee damage, End exit portal crashing the game, and End Poem crashing the client

Changes

Previous Behavior

• Hitting the Ender Dragon with a sword on a dedicated server did nothing. The dragon appeared immune to all melee damage.
• Entering the End exit portal after defeating the dragon crashed the game.
• The End Poem crashed the client on dedicated servers with an out-of-bounds access.

Root Cause

• Dragon melee: The server's entity ID allocator (smallId pool) assigned non-sequential IDs to the dragon's body parts (head, body, etc.), but the client assumed sequential offsets from the parent entity ID. Melee attacks targeted IDs the server didn't recognize, so hits were silently dropped.
• End portal: The player entity was never added to the Overworld level during the dimension transition. The addEntity call in PlayerList::changeDimension was gated behind a lastDimension != 1 check that excluded End-to-Overworld transitions, leaving the player as a ghost entity that caused a crash on the next interaction.
• End Poem: The WIN_GAME event handler indexed into localplayers[] using the server-assigned player index without bounds checking. On dedicated servers this index can exceed XUSER_MAX_COUNT, causing a null dereference.

Fix Implementation

• Dragon melee: ServerLevel::entityAdded() now reassigns sub-entity IDs to be sequential from the parent entity ID when an entity with parts is added to the level
• End portal: Removed the lastDimension != 1 gate so the player entity is always added to the destination level during End transitions
• End Poem: Added bounds check on the player index before accessing localplayers[], with a fallback to the primary local player

AI Use Disclosure

• No AI was used to write the code in this PR.

Related Issues

• None