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

tiles.toml

@@ -0,0 +1,61 @@
+# Floor tiles: IDs are used for texture lookup.
+# Weight: lower = faster to traverse (rock=50 is best, bedrock=150 is worst).
+# Stand flags: can_stand_in (air pocket), can_stand_on (solid surface), transparent (see-through).
+
+[floor_tiles.air]
+id = 0
+can_stand_in = true
+can_stand_on = false
+transparent = true
+astar_weight = 0
+
+[floor_tiles.grass]
+id = 1
+can_stand_in = false
+can_stand_on = true
+transparent = false
+astar_weight = 50
+
+[floor_tiles.dirt]
+id = 2
+can_stand_in = false
+can_stand_on = true
+transparent = false
+astar_weight = 50
+
+[floor_tiles.rock]
+id = 3
+can_stand_in = false
+can_stand_on = true
+transparent = false
+astar_weight = 50
+
+[floor_tiles.bedrock]
+id = 4
+can_stand_in = false
+can_stand_on = true
+transparent = false
+astar_weight = 50
+
+# Fixture tiles: walls and objects above floors.
+# IDs are relative to FIXTURE_ID_OFFSET (500000).
+
+[fixture_tiles.dirt_wall]
+id = 1
+solid = true
+
+[fixture_tiles.rock_wall]
+id = 2
+solid = true
+
+[fixture_tiles.bedrock_wall]
+id = 3
+solid = true
+
+[fixture_tiles.log]
+id = 4
+solid = false
+
+[fixture_tiles.leaves]
+id = 5
+solid = false