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/main.rs

@@ -148,7 +148,7 @@ fn mission_game(i: usize, progress: &campaign::Progress) -> (Game, Cam) {
     (g, cam)
 }
 
-const PROGRESS_KEY: &str = "dc.campaign";
+const PROGRESS_KEY: &str = "dc.campaign30"; // new key: the 30-mission order differs from the old one
 
 fn store_progress(p: &campaign::Progress) {
     platform::storage_set(PROGRESS_KEY, &serde_json::to_string(p).unwrap_or_default());