Fix: Add viewport scrolling to operation history

PROBLEM:
- History displayed ALL entries at once
- With many backups, first entries scroll off screen
- Cursor navigation worked but selection was invisible
- User had to "blindly" navigate 5+ entries to see anything

SOLUTION:
- Added viewport with max 15 visible items at once
- Viewport auto-scrolls to follow cursor position
- Scroll indicators show when there are more entries:
  * "▲ More entries above..."
  * "▼ X more entries below..."
- Cursor always visible within viewport

RESULT:
- ✅ Always see current selection
- ✅ Works with any number of history entries
- ✅ Clear visual feedback with scroll indicators
- ✅ Smooth navigation experience

internal/tui/history.go

@@ -19,6 +19,7 @@ type HistoryViewModel struct {
 	parent     tea.Model
 	history    []HistoryEntry
 	cursor     int
+	viewOffset int // For scrolling large lists
 }
 
 type HistoryEntry struct {
@@ -35,7 +36,8 @@ func NewHistoryView(cfg *config.Config, log logger.Logger, parent tea.Model) His
 		logger:     log,
 		parent:     parent,
 		history:    loadHistory(cfg),
-		cursor:  0, // Start at first item
+		cursor:     0,
+		viewOffset: 0, // Start at top
 	}
 }
 
@@ -104,11 +106,20 @@ func (m HistoryViewModel) Update(msg tea.Msg) (tea.Model, tea.Cmd) {
 		case "up", "k":
 			if m.cursor > 0 {
 				m.cursor--
+				// Scroll viewport up if cursor moves above visible area
+				if m.cursor < m.viewOffset {
+					m.viewOffset = m.cursor
+				}
 			}
 
 		case "down", "j":
 			if m.cursor < len(m.history)-1 {
 				m.cursor++
+				// Scroll viewport down if cursor moves below visible area
+				maxVisible := 15 // Show max 15 items at once
+				if m.cursor >= m.viewOffset+maxVisible {
+					m.viewOffset = m.cursor - maxVisible + 1
+				}
 			}
 		}
 	}
@@ -126,10 +137,26 @@ func (m HistoryViewModel) View() string {
 		s.WriteString(infoStyle.Render("📭 No backup history found"))
 		s.WriteString("\n\n")
 	} else {
+		maxVisible := 15 // Show max 15 items at once
+		
+		// Calculate visible range
+		start := m.viewOffset
+		end := start + maxVisible
+		if end > len(m.history) {
+			end = len(m.history)
+		}
+		
 		s.WriteString(fmt.Sprintf("Found %d backup operations (Viewing %d/%d):\n\n", 
 			len(m.history), m.cursor+1, len(m.history)))
 
-		for i, entry := range m.history {
+		// Show scroll indicators
+		if start > 0 {
+			s.WriteString(infoStyle.Render("  ▲ More entries above...\n"))
+		}
+
+		// Display only visible entries
+		for i := start; i < end; i++ {
+			entry := m.history[i]
 			line := fmt.Sprintf("[%s] %s - %s (%s)",
 				entry.Timestamp.Format("2006-01-02 15:04"),
 				entry.Type,
@@ -144,6 +171,12 @@ func (m HistoryViewModel) View() string {
 			}
 			s.WriteString("\n")
 		}
+		
+		// Show scroll indicator if more entries below
+		if end < len(m.history) {
+			s.WriteString(infoStyle.Render(fmt.Sprintf("  ▼ %d more entries below...\n", len(m.history)-end)))
+		}
+		
 		s.WriteString("\n")
 	}