feat(quiz): couples quiz with shareable watermarked results card

Replaces the notify-me quiz stub with a full loop: quiz sessions per
couple, answer-and-guess flow, dual-direction scoring, and a score-only
share card (no question or answer content) captured via ViewShot with
Sauci branding.

API: migration 0019 (quiz_questions, quiz_sessions, quiz_answers, 12
seeded questions), new quiz domain with session start / current /
answers / result routes, couple isolation, route + integration +
scoring unit tests.

Mobile: src/features/quiz feature (intro, per-question self+guess flow,
waiting-for-partner nudge, results with breakdown), quizStore with
sign-out clearing, QuizShareModal following SharePreviewModal, discovery
QuizTile, analytics events, and tests.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

apps/mobile/src/features/quiz/QuizScreen.tsx

@@ -0,0 +1,106 @@
+import { ActivityIndicator, View, StyleSheet } from "react-native";
+import { GradientBackground } from "../../components/ui";
+import { featureColors } from "../../theme";
+import { SwipeNoPartnerState } from "../swipe/components/SwipeNoPartnerState";
+import { useQuizScreen } from "./hooks/useQuizScreen";
+import {
+    QuizIntro,
+    QuizQuestionCard,
+    QuizResults,
+    QuizShareModal,
+    QuizWaitingState,
+} from "./components";
+
+export function QuizScreen() {
+    const {
+        screenState,
+        session,
+        result,
+        currentStep,
+        totalQuestions,
+        isStarting,
+        isSubmitting,
+        isLoadingResult,
+        shareModalVisible,
+        handleSelectOption,
+        handleStart,
+        handleNewQuiz,
+        handleRefresh,
+        handlePairPress,
+        handleNudgePartner,
+        openShareModal,
+        closeShareModal,
+    } = useQuizScreen();
+
+    if (screenState === "not_paired") {
+        return <SwipeNoPartnerState hasCouple={false} onPairPress={handlePairPress} />;
+    }
+
+    if (screenState === "loading") {
+        return (
+            <GradientBackground>
+                <View style={styles.loadingContainer}>
+                    <ActivityIndicator size="large" color={featureColors.quiz.accent} />
+                </View>
+            </GradientBackground>
+        );
+    }
+
+    if (screenState === "intro") {
+        return <QuizIntro isStarting={isStarting} onStart={handleStart} />;
+    }
+
+    if (screenState === "waiting") {
+        return <QuizWaitingState onNudgePartner={handleNudgePartner} onRefresh={handleRefresh} />;
+    }
+
+    if (screenState === "results") {
+        return (
+            <>
+                <QuizResults
+                    result={result}
+                    isLoadingResult={isLoadingResult}
+                    isStarting={isStarting}
+                    onNewQuiz={handleNewQuiz}
+                    onShare={openShareModal}
+                />
+                <QuizShareModal
+                    visible={shareModalVisible}
+                    onClose={closeShareModal}
+                    scorePercent={result?.score_percent ?? 0}
+                />
+            </>
+        );
+    }
+
+    // screenState === "answering"
+    if (!session || !currentStep || isSubmitting) {
+        return (
+            <GradientBackground>
+                <View style={styles.loadingContainer}>
+                    <ActivityIndicator size="large" color={featureColors.quiz.accent} />
+                </View>
+            </GradientBackground>
+        );
+    }
+
+    return (
+        <QuizQuestionCard
+            question={currentStep.question}
+            step={currentStep.step}
+            questionNumber={currentStep.questionNumber}
+            totalQuestions={totalQuestions}
+            onSelectOption={handleSelectOption}
+        />
+    );
+}
+
+const styles = StyleSheet.create({
+    loadingContainer: {
+        flex: 1,
+        justifyContent: "center",
+        alignItems: "center",
+    },
+});
+
+export default QuizScreen;