Aerie and flying creatures: bats, chain gargoyles, arcane owls, ember wyrms

- New room: aerie (key Y, rooms category, campaign from mission 7); flyers sleep there
- Arrivals: aerie 4+ bats; + torture chamber gargoyles; + library owls; big aerie and treasury
  (16+ each) a rare ember wyrm; portal checks free places in lairs and aerie separately
- Flyers cross water and lava (path finding, flag, attacks), are not burnt by lava, patrol far
  when idle, attack single enemies, flee to the aerie below 25% health and rest there up to 75%
- Owls shoot arcane bolts, the wyrm breathes fire with splash damage; shots from the air
- Hovering sprites with flapping, aerie floor, perches, roosts, plinths, twig and ember nests
- Room counts are recounted on load (no longer stored); tests for flying and arrivals

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

src/map.rs

@@ -57,6 +57,7 @@ pub enum Kind {
     Silver,     // silver vein: common, little value
     Ruby,       // ruby vein: rare, valuable
     Diamond,    // diamond vein: very rare, very valuable
+    Aerie,      // room for flying creatures (their beds)
 }
 
 // options for the map generator (campaign missions)
@@ -85,7 +86,7 @@ pub struct River {
 }
 
 // order matters for the packed savegame codec: only append new kinds
-const KINDS: [Kind; 23] = [
+const KINDS: [Kind; 24] = [
     Kind::Rock,
     Kind::Earth,
     Kind::Gold,
@@ -109,6 +110,7 @@ const KINDS: [Kind; 23] = [
     Kind::Silver,
     Kind::Ruby,
     Kind::Diamond,
+    Kind::Aerie,
 ];
 
 // treasures (veins, treasury content, imp loads): 0 gold, 1 silver, 2 ruby, 3 diamond
@@ -188,6 +190,7 @@ impl Tile {
                 | Kind::Bridge
                 | Kind::LavaBridge
                 | Kind::Shard
+                | Kind::Aerie
         )
     }
     // river tiles (open, but nobody can walk there)
@@ -620,6 +623,15 @@ impl Map {
         move |i| if self.t[i].walkable() { Some(1) } else { None }
     }
 
+    // flying creatures also cross water and lava
+    pub fn fly_cost(&self) -> impl Fn(usize) -> Option<u32> + '_ {
+        move |i| if self.t[i].walkable() || self.t[i].liquid() { Some(1) } else { None }
+    }
+
+    pub fn fly_path_to(&self, start: usize, target: usize) -> Option<Vec<usize>> {
+        self.search(start, self.fly_cost(), |i| i == target, true)
+    }
+
     pub fn hero_cost(&self) -> impl Fn(usize) -> Option<u32> + '_ {
         move |i| {
             let tl = &self.t[i];