1fix(fourislands): fill landlocked lake on NW island to fix port and b… (#4532)

Resolves #4531

## Description:

Fills the 462-pixel landlocked lake on the eastern shore of the
North-West island on the Four Islands map by coloring it with the
surrounding land color in image.png and recompiling the map assets. This
resolves gameplay bugs where ports built on this shore would face the
lake instead of the ocean (preventing warships from spawning into the
ocean) and transport ship routing to this shore was blocked due to the
lake being disconnected from the main ocean water component.
## Please complete the following:

- [x] I have added screenshots for all UI updates
- [ ] I process any text displayed to the user through translateText()
and I've added it to the en.json file
- [x] I have added relevant tests to the test directory

## Please put your Discord username so you can be contacted if a bug or
regression is found:

blontd6

<img width="1536" height="1448" alt="image"
src="https://github.com/user-attachments/assets/f6852d6f-78f8-4ca7-b5b3-c5d4475543e0"
/>

resources/maps/fourislands/manifest.json

@@ -3,17 +3,17 @@
   "id": "FourIslands",
   "map": {
     "height": 1500,
-    "num_land_tiles": 517044,
+    "num_land_tiles": 517506,
     "width": 1500
   },
   "map16x": {
     "height": 375,
-    "num_land_tiles": 31134,
+    "num_land_tiles": 31175,
     "width": 375
   },
   "map4x": {
     "height": 750,
-    "num_land_tiles": 127635,
+    "num_land_tiles": 127769,
     "width": 750
   },
   "multiplayer_frequency": 4,