Add initial character creation screen

Created the first version of the character creation feature, including the base layout and starting UI elements for customizing a character.

lib/character/types.ts

@@ -0,0 +1,5 @@
+import type { HSL } from "./color-utils";
+import type { CharacterLayerId } from "./presets";
+
+export type LayerColorState = Record<CharacterLayerId, HSL>;
+export type LayerVariantState = Record<CharacterLayerId, string>;