Add Guanabara Bay Map

## Purpose

Add a dedicated Guanabara Bay map to the game.

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## Objectives

- Add a 1680x1488 map covering the bay of Guanabara in Rio de Janeiro and the surrounding islands.
- The map has 1498664 land tiles.
- The map has 31 Nation Bots.

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## Description

Guanabara Bay is a coastal map centered on Rio de Janeiro, with a sheltered bay, mountainous terrain, narrow coastal plains, and scattered islands opening onto the Atlantic Ocean.

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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]

renan_ps

No files, tests, or entry points are named. Start by locating existing dedicated map implementations and the process for adding map dimensions, land tiles, and Nation Bots, then compare a similar coastal map. Done means adding the 1680x1488 Guanabara Bay map with 1,498,664 land tiles and 31 Nation Bots; the issue includes a reference image.

Written by the indexing model from the issue text.