Build English AI Coach starter app

src/services/mockAiCoach.ts

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+import type { EnglishLevel } from '../navigation/types';
+
+const examples: Record<EnglishLevel, string> = {
+  A1: 'Fast richtig! Correct: "I am learning English." Warum? Bei "I" nutzt du "am".',
+  A2: 'Good try. Correct: "I went to work yesterday." "Yesterday" braucht Past Tense.',
+  B1: 'Nice sentence. Alternative: "I have been practicing every day." Das klingt natuerlicher.',
+  B2: 'Strong idea. Improve flow: use linking words like "however", "therefore" or "in addition".',
+};
+
+export async function getMockAiReply(input: string, level: EnglishLevel) {
+  await new Promise((resolve) => setTimeout(resolve, 350));
+
+  if (!input.trim()) {
+    return 'Schreib einen kurzen englischen Satz, dann korrigiere ich ihn fuer dein Level.';
+  }
+
+  return `${examples[level]}\n\nDein Satz: "${input.trim()}"`;
+}