feat(01-03): implement level definitions 1-6 with finger mappings

- 6 levels per spec section 4.1 progression table
- Finger-to-CSS-variable mapping per spec section 8.3
- getLevelByNumber and getKeysUpToLevel helper functions
- All 14 tests passing

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

src/game/levels.ts

@@ -0,0 +1,110 @@
+import type { Level } from "../types";
+
+// Finger color CSS variable mapping per spec section 8.3
+// Left hand: pinky=Q/A/Y/1, ring=W/S/X/2, mid=E/D/C/3, index=R/F/V/T/G/B/4/5
+// Right hand: index=U/J/M/Z/H/N/6/7, mid=I/K/,/8, ring=O/L/./9, pinky=P/Ö/Ä/Ü/0/ß
+// Thumb: Space
+
+const fingerMap: Record<string, string> = {
+	// Left pinky
+	q: "--finger-l-pinky",
+	a: "--finger-l-pinky",
+	y: "--finger-l-pinky",
+	// Left ring
+	w: "--finger-l-ring",
+	s: "--finger-l-ring",
+	x: "--finger-l-ring",
+	// Left middle
+	e: "--finger-l-mid",
+	d: "--finger-l-mid",
+	c: "--finger-l-mid",
+	// Left index
+	r: "--finger-l-index",
+	f: "--finger-l-index",
+	v: "--finger-l-index",
+	t: "--finger-l-index",
+	g: "--finger-l-index",
+	b: "--finger-l-index",
+	// Right index
+	u: "--finger-r-index",
+	j: "--finger-r-index",
+	m: "--finger-r-index",
+	z: "--finger-r-index",
+	h: "--finger-r-index",
+	n: "--finger-r-index",
+	// Right middle
+	i: "--finger-r-mid",
+	k: "--finger-r-mid",
+	// Right ring
+	o: "--finger-r-ring",
+	l: "--finger-r-ring",
+	// Right pinky
+	p: "--finger-r-pinky",
+	ö: "--finger-r-pinky",
+	ä: "--finger-r-pinky",
+	ü: "--finger-r-pinky",
+	// Thumb
+	" ": "--finger-thumb",
+};
+
+export const levels: Level[] = [
+	{
+		level: 1,
+		newKeys: ["f", "j", " "],
+		allKeys: ["f", "j", " "],
+		fingerMap,
+	},
+	{
+		level: 2,
+		newKeys: ["d", "k"],
+		allKeys: ["f", "j", " ", "d", "k"],
+		fingerMap,
+	},
+	{
+		level: 3,
+		newKeys: ["s", "l"],
+		allKeys: ["f", "j", " ", "d", "k", "s", "l"],
+		fingerMap,
+	},
+	{
+		level: 4,
+		newKeys: ["a", "ö"],
+		allKeys: ["f", "j", " ", "d", "k", "s", "l", "a", "ö"],
+		fingerMap,
+	},
+	{
+		level: 5,
+		newKeys: ["g", "h"],
+		allKeys: ["f", "j", " ", "d", "k", "s", "l", "a", "ö", "g", "h"],
+		fingerMap,
+	},
+	{
+		level: 6,
+		newKeys: ["e", "i"],
+		allKeys: [
+			"f",
+			"j",
+			" ",
+			"d",
+			"k",
+			"s",
+			"l",
+			"a",
+			"ö",
+			"g",
+			"h",
+			"e",
+			"i",
+		],
+		fingerMap,
+	},
+];
+
+export function getLevelByNumber(n: number): Level | undefined {
+	return levels.find((l) => l.level === n);
+}
+
+export function getKeysUpToLevel(n: number): string[] {
+	const level = getLevelByNumber(n);
+	return level ? level.allKeys : [];
+}