docs: update README architecture diagram with magic_numbers locations

README.md

@@ -10,7 +10,31 @@ This is an **engine foundation**, not a complete game. Many features (crafting,
 src/
 ├── camera.rs          # Panning camera, z-level control (Q/E, scroll)
 ├── config.rs          # GameConfig, TileRegistry resources
-├── constants.rs       # Tile size, pathfinding constants
+├── constants.rs       # Tile size, structural constants
+├── entities/
+│   ├── item/magic_numbers.rs    # Item sprite constants
+│   ├── livestock/
+│   ├── sentient/
+│   └── shared_systems/
+│       ├── magic_numbers.rs     # Pathfinding + dig constants
+│       ├── occupancy.rs
+│       └── pathfinding.rs
+├── game.rs            # ZIndex resource, frame timing
+├── main.rs            # Bevy app bootstrap
+└── world/
+    ├── chunks/        # ChunkMap, chunk loading/unloading, connectivity
+    ├── generation/
+    │   ├── forestry/magic_numbers.rs  # Tree constants
+    │   ├── terrain/magic_numbers.rs   # Terrain + cave constants
+    │   ├── forestry.rs
+    │   └── terrain.rs
+    └── tiles/
+        ├── magic_numbers.rs          # A*, benchmark constants
+        ├── chunk_data.rs
+        ├── rendering.rs
+        ├── tilemap.rs
+        ├── tile_changed.rs
+        └── visibility.rs
 ├── entities/          # Dorfs, pigs, rabbits — ambulatory entities
 │   ├── sentient/
 │   ├── livestock/