Fix Bible reader page jumping and layout stability issues

Layout Stability Improvements:
- Add consistent minHeight (60vh) to content containers to prevent layout shifts
- Implement sticky navigation bar with smooth transitions
- Position loading spinner absolutely to prevent content jumping
- Add smooth opacity transitions during content loading

Content Loading Enhancements:
- Preserve previous verses during loading to prevent content flashing
- Display previous verse count during transitions for visual continuity
- Use requestAnimationFrame and setTimeout for smoother state transitions
- Implement content fade-in effects with reduced opacity during loading

Scroll Position Management:
- Store scroll position before loading new content
- Restore scroll position after content loads (maintains reading flow)
- Smart scroll restoration that only applies when not navigating to specific verse
- Prevent scroll jumping during chapter transitions

User Experience Improvements:
- Eliminate page "jumping" between chapter transitions
- Remove container resizing issues that disrupted reading flow
- Provide professional, book-like reading experience
- Maintain visual continuity during all navigation actions
- Smooth loading states with professional transitions

Technical Implementation:
- Add previousVerses state for content continuity
- Implement position: sticky for navigation stability
- Use CSS transitions for smooth visual effects
- Optimize loading timing with requestAnimationFrame
- Maintain consistent container dimensions throughout app lifecycle

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

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

app/[locale]/bible/reader.tsx

@@ -147,6 +147,7 @@ export default function BibleReaderNew() {
   const [preferences, setPreferences] = useState<ReadingPreferences>(defaultPreferences)
   const [highlightedVerse, setHighlightedVerse] = useState<number | null>(null)
   const [showScrollTop, setShowScrollTop] = useState(false)
+  const [previousVerses, setPreviousVerses] = useState<BibleVerse[]>([]) // Keep previous content during loading
 
   // Bookmark state
   const [isChapterBookmarked, setIsChapterBookmarked] = useState(false)
@@ -387,11 +388,35 @@ export default function BibleReaderNew() {
   useEffect(() => {
     if (selectedBook && selectedChapter) {
       setLoading(true)
+
+      // Store scroll position to prevent jumping
+      const scrollPosition = window.pageYOffset
+
       fetch(`/api/bible/verses?bookId=${selectedBook}&chapter=${selectedChapter}`)
         .then(res => res.json())
         .then(data => {
-          setVerses(data.verses || [])
-          setLoading(false)
+          const newVerses = data.verses || []
+
+          // Store previous verses before updating
+          setPreviousVerses(verses)
+
+          // Use requestAnimationFrame to ensure smooth transition
+          requestAnimationFrame(() => {
+            setVerses(newVerses)
+
+            // Small delay to allow content to render before removing loading state
+            setTimeout(() => {
+              setLoading(false)
+              setPreviousVerses([]) // Clear previous content after transition
+
+              // Restore scroll position if we're not navigating to a specific verse
+              const urlVerse = new URLSearchParams(window.location.search).get('verse')
+              if (!urlVerse) {
+                // Maintain scroll position for better UX
+                window.scrollTo({ top: Math.min(scrollPosition, document.body.scrollHeight), behavior: 'auto' })
+              }
+            }, 50) // Small delay for smoother transition
+          })
         })
         .catch(err => {
           console.error('Error fetching verses:', err)
@@ -808,7 +833,11 @@ export default function BibleReaderNew() {
         p: preferences.readingMode ? 1 : 2,
         ...getThemeStyles(),
         border: preferences.readingMode ? 'none' : `1px solid ${getThemeStyles().borderColor}`,
-        backgroundColor: preferences.readingMode ? 'transparent' : getThemeStyles().backgroundColor
+        backgroundColor: preferences.readingMode ? 'transparent' : getThemeStyles().backgroundColor,
+        position: 'sticky',
+        top: 0,
+        zIndex: 1,
+        transition: 'all 0.2s ease'
       }}
     >
       {/* First Row: Navigation Filters */}
@@ -1188,24 +1217,37 @@ export default function BibleReaderNew() {
           sx={{
             maxWidth: preferences.columnLayout ? 'none' : '800px',
             mx: 'auto',
-            width: '100%'
+            width: '100%',
+            minHeight: '60vh', // Prevent layout shifts
+            position: 'relative'
           }}
         >
-          {loading ? (
-            <Box sx={{ display: 'flex', justifyContent: 'center', py: 4 }}>
-              <CircularProgress />
-            </Box>
-          ) : (
-            <Paper
-              elevation={preferences.readingMode ? 0 : 1}
-              sx={{
-                ...getThemeStyles(),
-                borderRadius: preferences.readingMode ? 0 : 2,
-                p: preferences.readingMode ? 4 : 3,
-                minHeight: preferences.readingMode ? '100vh' : 'auto',
-                border: preferences.readingMode ? 'none' : `1px solid ${getThemeStyles().borderColor}`
-              }}
-            >
+          <Paper
+            elevation={preferences.readingMode ? 0 : 1}
+            sx={{
+              ...getThemeStyles(),
+              borderRadius: preferences.readingMode ? 0 : 2,
+              p: preferences.readingMode ? 4 : 3,
+              minHeight: preferences.readingMode ? '100vh' : '60vh', // Consistent minimum height
+              border: preferences.readingMode ? 'none' : `1px solid ${getThemeStyles().borderColor}`,
+              position: 'relative'
+            }}
+          >
+            {loading && (
+              <Box
+                sx={{
+                  position: 'absolute',
+                  top: '50%',
+                  left: '50%',
+                  transform: 'translate(-50%, -50%)',
+                  zIndex: 2
+                }}
+              >
+                <CircularProgress />
+              </Box>
+            )}
+
+            <Box sx={{ opacity: loading ? 0.3 : 1, transition: 'opacity 0.3s ease' }}>
               {/* Chapter Header */}
               <Box sx={{ mb: 4, textAlign: 'center' }}>
                 <Typography
@@ -1219,13 +1261,13 @@ export default function BibleReaderNew() {
                   {currentBook?.name} {selectedChapter}
                 </Typography>
                 <Typography variant="body2" color="text.secondary">
-                  {verses.length} {t('verses')}
+                  {(loading && previousVerses.length > 0 ? previousVerses : verses).length} {t('verses')}
                 </Typography>
               </Box>
 
               {/* Verses */}
               <Box sx={{ mb: 4 }}>
-                {verses.map(renderVerse)}
+                {(loading && previousVerses.length > 0 ? previousVerses : verses).map(renderVerse)}
               </Box>
 
               {/* Chapter Navigation */}
@@ -1248,8 +1290,8 @@ export default function BibleReaderNew() {
                   {t('nextChapter')}
                 </Button>
               </Box>
-            </Paper>
-          )}
+            </Box>
+          </Paper>
         </Box>
       </Container>