chore(tui): visual polish — detail sections, column headers, alert detail (#37)

## Summary

Bundled remaining UX polish items from the screenshot review.

### Changes

**Detail panel sections (#5)**
- Fields grouped into ENDPOINT, TIMING, HTTP, CONFIG sections with subtle headers
- Matches existing PROBE RESULTS and STATE CHANGES section pattern
- Cleaner visual hierarchy without box-drawing clutter

**Omit unconfigured fields (#6)**
- Timeout hidden when 0 (unconfigured)
- Method hidden when default GET
- AcceptedCodes shows "200-299" explicitly when empty

**Column header (#7)**
- `LATENCY` → `LAT` (design short, never truncate — htop/btop pattern)

**Alert detail view (#8)**
- `i` key on Alerts tab opens full detail panel
- Shows: type, health status, last sent time, send/fail counts, last error
- Full config key:value pairs (untruncated)
- Keybinding: `[i/Esc] Back  [e] Edit  [t] Test  [q] Quit`

### Files (3)
- `internal/tui/tab_sites.go` — section headers, field omission, LAT header
- `internal/tui/tab_alerts.go` — viewAlertDetailPanel()
- `internal/tui/tui.go` — stateAlertDetail, key handler, render routing

Reviewed-on: lerko/uptop#37

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"
@@ -40,19 +41,19 @@ func fmtMaintType(t string) string {
 	return maintStyle.Render("maintenance")
 }
 
-func fmtMaintMonitor(monitorID int, sites []models.Site) string {
+func fmtMaintMonitorW(monitorID int, sites []models.Site, maxW int) string {
 	if monitorID == 0 {
 		return "All"
 	}
 	for _, s := range sites {
 		if s.ID == monitorID {
-			return limitStr(s.Name, 18)
+			return limitStr(s.Name, maxW)
 		}
 	}
 	return fmt.Sprintf("#%d", monitorID)
 }
 
-func fmtMaintTime(t time.Time) string {
+func fmtMaintTime(t time.Time, colW int) string {
 	if t.IsZero() {
 		return subtleStyle.Render("—")
 	}
@@ -60,7 +61,10 @@ func fmtMaintTime(t time.Time) string {
 	if t.Year() == now.Year() && t.YearDay() == now.YearDay() {
 		return t.Format("15:04")
 	}
-	return t.Format("15:04 Jan 02")
+	if colW >= 14 {
+		return t.Format("15:04 Jan 02")
+	}
+	return t.Format("Jan 02")
 }
 
 func (m Model) isMonitorInMaintenance(monitorID int) bool {
@@ -92,8 +96,21 @@ func (m Model) viewMaintTab() string {
 		return "\n  No maintenance windows or incidents. Press [n] to create one."
 	}
 
+	var headers []string
+	var widths []int
+	if m.isWide() {
+		headers = []string{"#", "TITLE", "TYPE", "MONITORS", "STATUS", "STARTED", "ENDS"}
+		widths = []int{4, 24, 14, 22, 12, 16, 16}
+	} else {
+		headers = []string{"#", "TITLE", "TYPE", "MON", "ST", "START", "ENDS"}
+		widths = []int{4, 14, 13, 14, 11, 14, 14}
+	}
+	titleW := widths[1]
+	monW := widths[3]
+	timeW := widths[5]
+
 	return m.renderTable(
-		[]string{"#", "TITLE", "TYPE", "MONITORS", "STATUS", "STARTED", "ENDS"},
+		headers,
 		len(m.maintenanceWindows),
 		func(start, end int) [][]string {
 			var rows [][]string
@@ -102,17 +119,17 @@ 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),
+					fmtMaintMonitorW(mw.MonitorID, allSites, monW-2),
 					fmtMaintStatus(mw),
-					fmtMaintTime(mw.StartTime),
-					fmtMaintTime(mw.EndTime),
+					fmtMaintTime(mw.StartTime, timeW),
+					fmtMaintTime(mw.EndTime, timeW),
 				})
 			}
 			return rows
 		},
-		[]int{6, 0, 14, 20, 12, 16, 16},
+		widths,
 		nil,
 	)
 }