Fix minimap priority for impassable terrain pathfinding 🗺️ (#4361)

## Description:

Changes the minimap downscaling priority in the Go map generator from
`Impassable > Water > Land` to `Water > Impassable > Land`.

Tristar noticed this bug and reported it in the discord map-maker-area:

Previously, any 2x2 block containing even one impassable tile would
become impassable on the minimap, completely erasing narrow rivers
inside or bordering impassable terrain. Since the water pathfinder runs
on the minimap, this caused pathfinding failures near impassable
terrain.

With water taking highest priority, narrow rivers are preserved on the
minimap regardless of surrounding impassable terrain, ensuring the water
pathfinder can route through them correctly.

## Please complete the following:

- [X] I have added screenshots for all UI updates
- [X] 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:

FloPinguin

map-generator/map_generator.go

@@ -256,9 +256,9 @@ func convertToWebP(thumb ThumbData) ([]byte, error) {
 
 // createMiniMap downscales the terrain grid by half.
 // It maps 2x2 blocks of input tiles to a single output tile.
-// Priority: Impassable > Water > Land. If any of the 4 source tiles is
-// Impassable, the result is Impassable; else if any is Water, the result is
-// Water; otherwise the last Land tile wins.
+// Priority: Water > Impassable > Land. Water always wins so that narrow
+// rivers inside or bordering impassable terrain are preserved on the minimap
+// (the pathfinder runs on the minimap and needs accurate water bodies).
 func createMiniMap(tm [][]Terrain) [][]Terrain {
 	width := len(tm)
 	height := len(tm[0])
@@ -281,7 +281,16 @@ func createMiniMap(tm [][]Terrain) [][]Terrain {
 			}
 			src := tm[x][y]
 			dst := &miniMap[miniX][miniY]
-			// Impassable wins over everything; once set, keep it.
+			// Water wins over everything — narrow rivers must be preserved
+			// for pathfinding accuracy.
+			if dst.Type == Water {
+				continue
+			}
+			if src.Type == Water {
+				*dst = src
+				continue
+			}
+			// Impassable wins over land; once set, keep it.
 			if dst.Type == Impassable {
 				continue
 			}
@@ -289,10 +298,6 @@ func createMiniMap(tm [][]Terrain) [][]Terrain {
 				*dst = src
 				continue
 			}
-			// Water wins over land; once set to water, keep it.
-			if dst.Type == Water {
-				continue
-			}
 			*dst = src
 		}
 	}