fix(mobile): prevent onboarding tooltip from overflowing screen

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

packages/client-mobile/src/components/OnboardingTour.vue

@@ -46,7 +46,7 @@ const highlightStyle = computed(() => {
   };
 });
 
-// Tooltip position
+// Tooltip position with boundary check
 const tooltipStyle = computed(() => {
   const step = props.steps[props.currentStep];
   if (!step) return {};
@@ -63,24 +63,41 @@ const tooltipStyle = computed(() => {
   const pos = step.position || 'bottom';
   const rect = targetRect.value;
   const gap = 16;
+  const margin = 16; // Screen edge margin
+  const tooltipWidth = 300;
+  const screenWidth = window.innerWidth;
+
+  // Calculate horizontal position with boundary check
+  function getHorizontalPosition() {
+    const centerX = rect.left + rect.width / 2;
+    let left = centerX - tooltipWidth / 2;
+
+    // Check left boundary
+    if (left < margin) {
+      left = margin;
+    }
+    // Check right boundary
+    if (left + tooltipWidth > screenWidth - margin) {
+      left = screenWidth - margin - tooltipWidth;
+    }
+    return `${left}px`;
+  }
 
   switch (pos) {
     case 'top':
       return {
         bottom: `${window.innerHeight - rect.top + gap}px`,
-        left: `${rect.left + rect.width / 2}px`,
-        transform: 'translateX(-50%)',
+        left: getHorizontalPosition(),
       };
     case 'bottom':
       return {
         top: `${rect.bottom + gap}px`,
-        left: `${rect.left + rect.width / 2}px`,
-        transform: 'translateX(-50%)',
+        left: getHorizontalPosition(),
       };
     case 'left':
       return {
         top: `${rect.top + rect.height / 2}px`,
-        right: `${window.innerWidth - rect.left + gap}px`,
+        right: `${screenWidth - rect.left + gap}px`,
         transform: 'translateY(-50%)',
       };
     case 'right':