Add New Guinea Map

## Purpose

Add a dedicated New Guinea map to the game.

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## Objectives

- Add a 2304x1196 map covering the main island of New Guinea and major surrounding islands.
- The map has approximately 568k land tiles.
- Design the map primarily for 2-team games, divided between the western and eastern halves of the island.
- Keep the playable land distribution close to even between both sides, currently approximately 49.9% / 50.1%.
- Include around 10 Nation Bots.

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## Description

New Guinea is a large, horizontally shaped island with mountainous terrain through the central part of the island, long northern and southern coastlines, and several surrounding islands.

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## Assignment

- [x] I'd like to be assigned to this issue and work on it myself

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[Discord Name if Different]

.016419

The issue names no files, tests, or entry points. Start by locating existing map definitions and assets in OpenFrontIO, then compare a similar map's integration and validation steps. Done means the New Guinea map is playable at 2304x1196, has roughly 568k land tiles, near-even two-team land distribution, and around 10 Nation Bots.

Written by the indexing model from the issue text.