fix(tutorial): reduce tooltip z-index to scroll under nav bar

Change tutorial tooltip z-index from 1000 to 50 so it scrolls under the
app nav bar (z-index 100) along with the abacus. This prevents the coaching
text from appearing layered above the nav while the abacus it points to is
hidden beneath it.

🤖 Generated with [Claude Code](https://claude.com/claude-code)

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

apps/web/src/components/tutorial/TutorialPlayer.tsx

@@ -640,7 +640,7 @@ function TutorialPlayerContent({
                   maxWidth: '200px',
                   minWidth: '150px',
                   wordBreak: 'break-word',
-                  zIndex: 1000,
+                  zIndex: 50,
                   opacity: 0.95,
                   transition: 'all 0.3s ease',
                   transform: showCelebration ? 'scale(1.05)' : 'scale(1)',