feat(tui): responsive table layout for all tabs

Extract shared computeTableLayout() into table_helpers.go — takes column
definitions with short/full headers, min/max widths, and a flex column
that absorbs surplus space. All tabs now use it:

- Alerts: CONFIG column is flex, NAME/TYPE/SENT expand with width
- Maint: TITLE column is flex, TYPE/MONITORS/STATUS/dates expand
- Nodes: NAME column is flex, REGION/LAST SEEN/VERSION expand
- Users: PUBLIC KEY column is flex, USERNAME expands
- Sites: uses same colDef type (keeps special dual-flex for NAME+HISTORY)

Headers auto-switch short/full based on available width across all tabs.

internal/tui/tab_maint.go

@@ -2,10 +2,11 @@ package tui
 
 import (
 	"fmt"
-	"gitea.lerkolabs.com/lerko/uptop/internal/models"
 	"strconv"
 	"time"
 
+	"gitea.lerkolabs.com/lerko/uptop/internal/models"
+
 	tea "github.com/charmbracelet/bubbletea"
 	"github.com/charmbracelet/huh"
 	"github.com/charmbracelet/lipgloss"
@@ -92,8 +93,20 @@ func (m Model) viewMaintTab() string {
 		return "\n  No maintenance windows or incidents. Press [n] to create one."
 	}
 
+	cols := []colDef{
+		{"#", "#", 4, 4, false},
+		{"TITLE", "TITLE", 12, 28, true},
+		{"TYPE", "TYPE", 10, 14, false},
+		{"MON", "MONITORS", 10, 20, false},
+		{"STATUS", "STATUS", 8, 12, false},
+		{"START", "STARTED", 10, 16, false},
+		{"ENDS", "ENDS", 10, 16, false},
+	}
+	headers, widths := m.computeTableLayout(cols, 0)
+	titleW := widths[1]
+
 	return m.renderTable(
-		[]string{"#", "TITLE", "TYPE", "MONITORS", "STATUS", "STARTED", "ENDS"},
+		headers,
 		len(m.maintenanceWindows),
 		func(start, end int) [][]string {
 			var rows [][]string
@@ -102,7 +115,7 @@ func (m Model) viewMaintTab() string {
 				mw := m.maintenanceWindows[i]
 				rows = append(rows, []string{
 					strconv.Itoa(i + 1),
-					m.zones.Mark(fmt.Sprintf("maint-%d", i), limitStr(mw.Title, 24)),
+					m.zones.Mark(fmt.Sprintf("maint-%d", i), limitStr(mw.Title, titleW-2)),
 					fmtMaintType(mw.Type),
 					fmtMaintMonitor(mw.MonitorID, allSites),
 					fmtMaintStatus(mw),
@@ -112,7 +125,7 @@ func (m Model) viewMaintTab() string {
 			}
 			return rows
 		},
-		[]int{6, 0, 14, 20, 12, 16, 16},
+		widths,
 		nil,
 	)
 }