Rivers and bridges: water and lava tiles, bridge tool, burning in lava

- New tile kinds (appended for the savegame codec): water, lava, wooden bridge, stone bridge, core shard
- Sunken river beds with banks, bridge decks with rails, lava glow and lights
- Bridge tool (key U, rooms category): bridges grow from own ground, 30 gold/tile over water, 75 over lava
- Selling a bridge drops the units on it into the river (water: swim to the bank, lava: burn)
- Cannon blasts and punches knock units back; into lava = burnt (heroes still pay their bounty)
- Heroes cannot path through rivers; texts EN/DE; tests for bridges and lava

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

src/map.rs

@@ -49,10 +49,15 @@ pub enum Kind {
     Torture,
     Tower, // floor tile occupied by a defence tower (not walkable)
     Temple,
+    Water,      // underground river: not walkable, needs a bridge
+    Lava,       // lava river: not walkable, burns what falls in
+    Bridge,     // wooden bridge over water (walkable)
+    LavaBridge, // stone bridge over lava (walkable)
+    Shard,      // floor with a shard of the soul core (campaign)
 }
 
 // order matters for the packed savegame codec: only append new kinds
-const KINDS: [Kind; 15] = [
+const KINDS: [Kind; 20] = [
     Kind::Rock,
     Kind::Earth,
     Kind::Gold,
@@ -68,6 +73,11 @@ const KINDS: [Kind; 15] = [
     Kind::Torture,
     Kind::Tower,
     Kind::Temple,
+    Kind::Water,
+    Kind::Lava,
+    Kind::Bridge,
+    Kind::LavaBridge,
+    Kind::Shard,
 ];
 
 #[derive(Clone, Copy, PartialEq, Eq, Debug, Serialize, Deserialize)]
@@ -117,9 +127,36 @@ impl Tile {
     pub fn walkable(&self) -> bool {
         matches!(
             self.kind,
-            Kind::Floor | Kind::Treasury | Kind::Lair | Kind::Farm | Kind::Training | Kind::Library | Kind::Portal | Kind::Gate | Kind::Torture | Kind::Temple
+            Kind::Floor
+                | Kind::Treasury
+                | Kind::Lair
+                | Kind::Farm
+                | Kind::Training
+                | Kind::Library
+                | Kind::Portal
+                | Kind::Gate
+                | Kind::Torture
+                | Kind::Temple
+                | Kind::Bridge
+                | Kind::LavaBridge
+                | Kind::Shard
         )
     }
+    // river tiles (open, but nobody can walk there)
+    pub fn liquid(&self) -> bool {
+        matches!(self.kind, Kind::Water | Kind::Lava)
+    }
+    pub fn bridge(&self) -> bool {
+        matches!(self.kind, Kind::Bridge | Kind::LavaBridge)
+    }
+    // the river below a bridge or river tile
+    pub fn river(&self) -> Option<Kind> {
+        match self.kind {
+            Kind::Water | Kind::Bridge => Some(Kind::Water),
+            Kind::Lava | Kind::LavaBridge => Some(Kind::Lava),
+            _ => None,
+        }
+    }
 }
 
 pub fn idx(x: i32, y: i32) -> usize {
@@ -441,7 +478,7 @@ impl Map {
                 Kind::Earth if tl.reinforced => Some(70),
                 Kind::Earth => Some(7),
                 Kind::Gold => Some(12),
-                Kind::Rock | Kind::Core | Kind::Tower => None,
+                Kind::Rock | Kind::Core | Kind::Tower | Kind::Water | Kind::Lava => None,
                 _ => Some(1),
             }
         }