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/menu.rs

@@ -1174,5 +1174,8 @@ pub fn goal_text(g: Goal) -> String {
         Goal::Loot(n) => trf("goal.loot", &[n.to_string()]),
         Goal::Towers => tr("goal.towers"),
         Goal::Survive(n) => trf("goal.survive", &[n.to_string()]),
+        Goal::Rivals => tr("goal.rivals"),
+        Goal::Springs(n) => trf("goal.springs", &[n.to_string()]),
+        Goal::Freed(n) => trf("goal.freed", &[n.to_string()]),
     }
 }