fix(pathfinding): correct BinaryHeap ordering and movement threshold

- Fix PathNode and ChunkPathNode Ord impl to use correct min-heap ordering
  (self.f_score.cmp vs other.f_score.cmp) - was causing zig-zag paths
- Fix movement threshold formula to use tile_weight directly
  (walk_speed * tile_weight / 50) instead of inverted multiplier
- Update comments to reflect 'higher = slower to traverse' semantics

src/entities/shared_systems/pathfinding.rs

@@ -155,10 +155,9 @@ struct PathNode {
 
 impl Ord for PathNode {
     fn cmp(&self, other: &Self) -> std::cmp::Ordering {
-        other
-            .f_score
-            .cmp(&self.f_score)
-            .then_with(|| other.g_score.cmp(&self.g_score))
+        self.f_score
+            .cmp(&other.f_score)
+            .then_with(|| self.g_score.cmp(&other.g_score))
     }
 }
 
@@ -508,8 +507,7 @@ pub fn movement(mut query: Query<(&mut Ambulatory, &mut Transform)>, tilemap: Re
 
             if ambulatory.walk_speed > 0. {
                 let tile_weight = get_tile_weight(&tilemap, current_pos.as_ivec3());
-                let speed_multiplier = (tile_weight as f32) / 50.0;
-                let threshold = (ambulatory.walk_speed * speed_multiplier) as u32;
+                let threshold = (ambulatory.walk_speed as i32 * tile_weight as i32 / 50) as u32;
 
                 if ambulatory.step_recovery <= threshold {
                     ambulatory.step_recovery += 1;
@@ -557,7 +555,7 @@ fn is_standable_tile(tilemap: &TileMap, pos: IVec3) -> bool {
     tilemap.is_standable(pos)
 }
 
-/// Get the A* weight for a tile position. Lower is better (faster to traverse).
+/// Get the A* weight for a tile position. Higher = slower to traverse.
 /// Returns 100 (default) if tile not found.
 #[inline]
 fn get_tile_weight(tilemap: &TileMap, pos: IVec3) -> u8 {
@@ -566,7 +564,7 @@ fn get_tile_weight(tilemap: &TileMap, pos: IVec3) -> u8 {
 
 /// Calculate movement cost including tile weight.
 /// Base costs: cardinal=10, diagonal=14, vertical~50.
-/// Tile weight adds: (weight - 50) / 5 to make heavier tiles more costly.
+/// Tile weight adds: (weight - 50) / 5 to make higher-weight tiles more costly.
 fn calculate_movement_cost(move_dir: IVec3, tile_weight: u8) -> i32 {
     let base_cost = match (
         move_dir.x.abs() / ITILE_SIZE,
@@ -851,10 +849,9 @@ impl PartialEq for ChunkPathNode {
 
 impl Ord for ChunkPathNode {
     fn cmp(&self, other: &Self) -> std::cmp::Ordering {
-        other
-            .f_score
-            .cmp(&self.f_score)
-            .then_with(|| other.g_score.cmp(&self.g_score))
+        self.f_score
+            .cmp(&other.f_score)
+            .then_with(|| self.g_score.cmp(&other.g_score))
     }
 }