Add minimal Bluegill fishing loop

inventory/fish_inventory.gd

@@ -0,0 +1,21 @@
+class_name FishInventory
+extends Node
+
+const FishDataType = preload("res://fish/fish_data.gd")
+
+signal contents_changed(fish_id: StringName, count: int)
+
+var _fish_counts: Dictionary[StringName, int] = {}
+
+
+func add_fish(fish: FishDataType, amount: int = 1) -> void:
+	if fish == null or fish.id.is_empty() or amount <= 0:
+		return
+
+	var new_count: int = get_count(fish.id) + amount
+	_fish_counts[fish.id] = new_count
+	contents_changed.emit(fish.id, new_count)
+
+
+func get_count(fish_id: StringName) -> int:
+	return _fish_counts.get(fish_id, 0)