Campaign of 30 missions: six against the rival masters Mossgrim and Lady Nightwell, islands, mana springs, sealed caves with chained creatures

- missions interleaved into one story (EN/DE), new epilogue, map sizes grow to 176x176
- islands in water or lava with treasure and/or a mana spring; rivers at least four tiles wide
- sealed caves with treasure and a chained creature that joins once the cave is claimed
- new goals: rival cores, mana springs, freed creatures
- rival messages name the masters; new progress key for the new mission order

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

src/render3d.rs

@@ -1805,6 +1805,7 @@ pub fn minimap_color(tile: &Tile) -> [u8; 4] {
         Kind::Shard => [255, 60, 120, 255],
         Kind::Aerie => [170, 140, 90, 255],
         Kind::Steel => [150, 160, 180, 255],
+        Kind::ManaSpring => [90, 230, 255, 255],
     }
 }