refactor(tui): extract shared table rendering, fix cursor bounds

- New table_helpers.go with renderTable() and shared styles
- Remove 4 duplicated style blocks (header/cell/selected/border)
  from tab_alerts.go and tab_users.go
- All 3 tab views now use renderTable() for offset/end calc,
  selected row highlighting, and table construction
- Sites tab keeps siteGroupStyle via StyleOverride callback
- Clamp cursor to list length at end of refreshData() to prevent
  index-out-of-bounds after concurrent list changes
- Fix off-by-one in tab click handler (i <= maxTabs → i < tabCount)

internal/tui/tab_users.go

@@ -6,26 +6,6 @@ import (
 
 	tea "github.com/charmbracelet/bubbletea"
 	"github.com/charmbracelet/huh"
-	"github.com/charmbracelet/lipgloss"
-	"github.com/charmbracelet/lipgloss/table"
-)
-
-var (
-	userHeaderStyle = lipgloss.NewStyle().
-			Foreground(lipgloss.Color("#7D56F4")).
-			Bold(true).
-			Padding(0, 1)
-
-	userCellStyle = lipgloss.NewStyle().Padding(0, 1)
-
-	userSelectedStyle = lipgloss.NewStyle().
-				Padding(0, 1).
-				Bold(true).
-				Foreground(lipgloss.Color("#ffffff")).
-				Background(lipgloss.Color("#3b3b5c"))
-
-	userBorderStyle = lipgloss.NewStyle().
-			Foreground(lipgloss.Color("#444"))
 )
 
 type userFormData struct {
@@ -53,46 +33,24 @@ func (m Model) viewUsersTab() string {
 		return "\n  No users configured. Press [n] to add one."
 	}
 
-	end := m.tableOffset + m.maxTableRows
-	if end > len(m.users) {
-		end = len(m.users)
-	}
-
-	selectedVisual := m.cursor - m.tableOffset
-
-	var rows [][]string
-	for i := m.tableOffset; i < end; i++ {
-		u := m.users[i]
-		rows = append(rows, []string{
-			fmt.Sprintf("%d", i+1),
-			m.zones.Mark(fmt.Sprintf("user-%d", i), limitStr(u.Username, 15)),
-			fmtRole(u.Role),
-			fmtKey(u.PublicKey),
-		})
-	}
-
-	tableWidth := m.termWidth - 6
-	if tableWidth < 40 {
-		tableWidth = 40
-	}
-
-	t := table.New().
-		Border(lipgloss.RoundedBorder()).
-		BorderStyle(userBorderStyle).
-		Width(tableWidth).
-		Headers("#", "USERNAME", "ROLE", "PUBLIC KEY").
-		Rows(rows...).
-		StyleFunc(func(row, col int) lipgloss.Style {
-			if row == table.HeaderRow {
-				return userHeaderStyle
+	return m.renderTable(
+		[]string{"#", "USERNAME", "ROLE", "PUBLIC KEY"},
+		len(m.users),
+		func(start, end int) [][]string {
+			var rows [][]string
+			for i := start; i < end; i++ {
+				u := m.users[i]
+				rows = append(rows, []string{
+					fmt.Sprintf("%d", i+1),
+					m.zones.Mark(fmt.Sprintf("user-%d", i), limitStr(u.Username, 15)),
+					fmtRole(u.Role),
+					fmtKey(u.PublicKey),
+				})
 			}
-			if row == selectedVisual {
-				return userSelectedStyle
-			}
-			return userCellStyle
-		})
-
-	return "\n" + t.Render()
+			return rows
+		},
+		nil, nil,
+	)
 }
 
 func (m *Model) initUserHuhForm() tea.Cmd {