feat: data-oriented chunks optimization with tile registry

- Phase 1: Bit-packed standability (ChunkData with bitsets)
- Phase 2: Reactive connectivity (dirty chunks)
- Phase 3: Async terrain baking (AsyncComputeTaskPool)
- Pathfinding weight system (rock=50 preferred, bedrock=150 avoided)
- Movement speed affected by tile weight
- External tiles.toml for hot-reloadable tile definitions
- TileRegistry singleton for async-safe tile lookups
- Fixed world_to_chunk to use CHUNK_SIZE_TILE (128) not CHUNK_SIZE (8)
- Fixed infinite spawner with Local<bool> state guards
- Fixed spawn coordinate grid alignment

Note: Zigzag pathfinding bug introduced - needs investigation

src/entities/livestock/pig.rs

@@ -3,6 +3,7 @@ use crate::constants::TILE_SIZE;
 use crate::constants::*;
 use crate::entities::item::{spawn_prefab, MiscPrefab};
 use crate::entities::shared_components::Ambulatory;
+use crate::game::SpawnDelay;
 use crate::world::tiles::tilemap;
 use crate::world::VisibleGameEntity;
 use bevy::prelude::*;
@@ -36,7 +37,7 @@ impl Pig {
             },
             transform: Transform::from_translation(position).with_scale(Vec3::splat(PIXEL_RATIO)),
             visibility: Visibility::Hidden,
-            drop_timer: PigDropTimer(Timer::from_seconds(5.0, TimerMode::Repeating)), // NEW
+            drop_timer: PigDropTimer(Timer::from_seconds(5.0, TimerMode::Repeating)),
         }
     }
 }
@@ -49,18 +50,30 @@ pub fn spawn_pigs(
     asset_server: Res<AssetServer>,
     mut rng_q: Query<&mut WyRand, With<GlobalRng>>,
     config: Res<GameConfig>,
+    mut delay: ResMut<SpawnDelay>,
+    mut has_spawned: Local<bool>,
 ) {
+    if *has_spawned {
+        return;
+    }
+
+    if delay.0 < 60 {
+        delay.0 += 1;
+        return;
+    }
+
+    *has_spawned = true;
+
     if let Ok(mut rng) = rng_q.single_mut() {
         for _ in 0..config.spawn_counts.pigs {
+            let raw_x = rng.random_range(-32.0f32..32.0f32);
+            let raw_y = rng.random_range(-32.0f32..32.0f32);
+            let grid_x = (raw_x / TILE_SIZE).round() * TILE_SIZE;
+            let grid_y = (raw_y / TILE_SIZE).round() * TILE_SIZE;
+            let grid_z = 35.0 * TILE_SIZE;
+
             let pig = commands
-                .spawn(Pig::new(
-                    &asset_server,
-                    Vec3::new(
-                        rng.random_range(-32.0f32..32.0f32).round(),
-                        rng.random_range(-32.0f32..32.0f32).round(),
-                        35.0,
-                    ) * TILE_SIZE,
-                ))
+                .spawn(Pig::new(&asset_server, Vec3::new(grid_x, grid_y, grid_z)))
                 .id();
             commands.entity(pig).insert(VisibleGameEntity);
         }