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/campaign.rs

@@ -9,8 +9,8 @@ use serde::{Deserialize, Serialize};
 
 // From which mission (0-based) on each tool is available (same order as ui::TOOLS):
 // dig, hand, treasury, lair, farm, training, library, sell, flag, lightning, heal, imp,
-// torture, temple, arrow tower, cannon tower, magic tower, bridge
-pub const TOOL_UNLOCK: [usize; 18] = [0, 0, 0, 0, 0, 2, 4, 0, 0, 3, 4, 0, 6, 9, 3, 5, 9, 1];
+// torture, temple, arrow tower, cannon tower, magic tower, bridge, aerie
+pub const TOOL_UNLOCK: [usize; 19] = [0, 0, 0, 0, 0, 2, 4, 0, 0, 3, 4, 0, 6, 9, 3, 5, 9, 1, 6];
 
 pub struct FortDef {
     pub at: (f32, f32), // centre as a fraction of the map size