feat(03-01): implement word lists per level with getWordsForLevel

- Static word lists for levels 1-6, 8-10 words each
- Levels 1-2 use letter combos (no real words possible with F/J/D/K)
- Levels 3-6 mix real German words with combos
- All words validated: only use learned letters, max 5 chars
- getWordsForLevel with/without replacement sampling
- All 8 tests pass

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

src/game/words.ts

@@ -0,0 +1,64 @@
+import { getKeysUpToLevel } from "./levels";
+
+/**
+ * Word lists per level.
+ * Levels 1-2: Only F/J/D/K available -- no real German words possible, use letter combos.
+ * Levels 3+: Mix of real German words and combos using only learned letters.
+ * All words max 5 characters, no spaces.
+ */
+export const wordsByLevel: Record<number, string[]> = {
+	// Level 1: f, j
+	1: ["ff", "jj", "fj", "jf", "fjf", "jfj", "fjfj", "jfjf", "ffj", "jjf"],
+	// Level 2: f, j, d, k
+	2: ["fdk", "kdf", "djf", "fkd", "dkf", "jdk", "kfj", "dfjk", "kjdf", "fkjd"],
+	// Level 3: f, j, d, k, s, l
+	3: ["sdf", "sdk", "lsd", "flsk", "sldf", "dsl", "kls", "flds", "jskl", "lkds"],
+	// Level 4: f, j, d, k, s, l, a, ö -- "aas", "das", "lass", "als" are real words
+	4: ["als", "das", "aas", "lass", "fad", "dal", "lad", "alfa", "salö", "aöds"],
+	// Level 5: f, j, d, k, s, l, a, ö, g, h -- "lag", "sah", "glas" are real words
+	5: ["glas", "lag", "gah", "hag", "gal", "sah", "hals", "has", "gash", "flags"],
+	// Level 6: f, j, d, k, s, l, a, ö, g, h, e, i -- "eis", "die", "sie", "lied", "fies"
+	6: ["eis", "die", "sie", "lied", "fies", "dies", "sei", "geld", "held", "lieh"],
+};
+
+/**
+ * Returns `count` random words from the given level's word list.
+ * If count <= list length: sampling without replacement.
+ * If count > list length: sampling with replacement.
+ * Returns empty array for non-existent levels.
+ */
+export function getWordsForLevel(level: number, count: number): string[] {
+	const list = wordsByLevel[level];
+	if (!list || list.length === 0) return [];
+
+	if (count <= list.length) {
+		// Shuffle and take first `count` (without replacement)
+		const shuffled = [...list];
+		for (let i = shuffled.length - 1; i > 0; i--) {
+			const j = Math.floor(Math.random() * (i + 1));
+			[shuffled[i], shuffled[j]] = [shuffled[j]!, shuffled[i]!];
+		}
+		return shuffled.slice(0, count);
+	}
+
+	// With replacement
+	const result: string[] = [];
+	for (let i = 0; i < count; i++) {
+		result.push(list[Math.floor(Math.random() * list.length)]!);
+	}
+	return result;
+}
+
+// Validation helper (used in tests)
+export function validateWordList(): boolean {
+	for (const [levelStr, words] of Object.entries(wordsByLevel)) {
+		const level = Number(levelStr);
+		const allowedKeys = getKeysUpToLevel(level).filter((k) => k !== " ");
+		for (const word of words) {
+			for (const char of word) {
+				if (!allowedKeys.includes(char)) return false;
+			}
+		}
+	}
+	return true;
+}