refactor(tui): two-tier responsive table layout (compact/wide at 120 cols)

Replace continuous surplus distribution with two fixed layouts per table.
Breakpoint at 120 columns — matches how btop/k9s do it.

Compact (<120): short headers (LAT, UP%, RT, ST, MON, SENT, VER),
  tight fixed widths, no surplus guessing.

Wide (≥120): full headers (LATENCY, UPTIME, RETRIES, STATUS, MONITORS,
  LAST SENT, VERSION), generous widths.

Sites tab keeps content-aware NAME sizing + sparkline flex.
All other tabs (Alerts, Maint, Nodes, Users) use simple fixed tiers.

Removed old computeTableLayout/colDef/tierCol/pickTier — no longer needed.

internal/tui/tab_alerts.go

@@ -148,23 +148,17 @@ func (m Model) viewAlertsTab() string {
 		return "\n  No alert channels configured. Press [n] to add one."
 	}
 
-	maxName := 0
-	for _, a := range m.alerts {
-		if n := len([]rune(a.Name)); n > maxName {
-			maxName = n
-		}
+	var headers []string
+	var widths []int
+	if m.isWide() {
+		headers = []string{"#", "", "NAME", "TYPE", "CONFIG", "LAST SENT"}
+		widths = []int{4, 3, 18, 12, 40, 12}
+	} else {
+		headers = []string{"#", "", "NAME", "TYPE", "CONFIG", "SENT"}
+		widths = []int{4, 3, 14, 10, 24, 8}
 	}
-
-	cols := []colDef{
-		{"#", "#", 4, 4, false},
-		{"", "", 3, 3, false},
-		{"NAME", "NAME", 10, 20, false},
-		{"TYPE", "TYPE", 10, 12, false},
-		{"CONFIG", "CONFIG", 15, 40, true},
-		{"SENT", "LAST SENT", 8, 12, false},
-	}
-	headers, widths := m.computeTableLayout(cols, 0)
 	nameW := widths[2]
+	cfgW := widths[4]
 
 	return m.renderTable(
 		headers,
@@ -179,10 +173,10 @@ func (m Model) viewAlertsTab() string {
 					fmtAlertHealth(h),
 					m.zones.Mark(fmt.Sprintf("alert-%d", i), limitStr(a.Name, nameW-2)),
 					fmtAlertType(a.Type),
-					fmtAlertConfig(struct {
+					limitStr(fmtAlertConfig(struct {
 						Type     string
 						Settings map[string]string
-					}{a.Type, a.Settings}),
+					}{a.Type, a.Settings}), cfgW-2),
 					fmtAlertLastSent(h),
 				})
 			}