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/lib/analytics.ts

@@ -273,6 +273,12 @@ export const Events = {
   // Invite events
   inviteCodeCopied: () => logEvent("invite_code_copied"),
 
+  // Quiz events
+  quizStarted: () => logEvent("quiz_started"),
+  quizCompleted: (scorePercent: number) => logEvent("quiz_completed", { score_percent: scorePercent }),
+  quizShared: () => logEvent("quiz_shared"),
+  quizPartnerNudged: () => logEvent("quiz_partner_nudged"),
+
   // Tutorial events
   tutorialStarted: (tutorial: "swipe" | "matches") =>
     logEvent("tutorial_started", { tutorial }),