feat: support global coordinates for maps larger than 256x256

[mrallanodreman]

Summary

Adds a backward-compatible global-coordinate path for maps larger than 256x256.

• Introduces ushort-based global Point/terrain/pathfinding and EF persistence migration.
• Adds global movement, map-change, respawn, scope, NPC and character-information packets while retaining legacy packets for coordinates <= 255.
• Adds generated packet bindings, boundary tests, coordinate tests and protocol documentation.

Verification

• Network packet project: 0 errors, 0 warnings.
• GameServer build: 0 errors; existing analyzer/style warnings remain.
• GlobalPacketHeaderTests: 1/1.
• WorldCoordinatesTest: 4/4.
• Runtime fork verification: World1 512x512 movement/render across 255 -> 256.

The feature is intentionally isolated from the companion implementation in the fork.