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

Detail panel:
- Grouped fields into sections (ENDPOINT, TIMING, HTTP, CONFIG)
- Omit Timeout when 0 (unconfigured)
- Omit Method when default GET
- Show explicit "200-299" when AcceptedCodes empty

Table:
- LATENCY header → LAT (design short, never truncate)

Alerts:
- Press [i] for alert detail panel: full config, health status,
  send counts, last error
- Keybinding display updated with [i]Info

Bundled remaining UX polish items from screenshot review.

internal/tui/tab_sites.go

@@ -378,7 +378,7 @@ func (m Model) viewSitesTab() string {
 
 	var groupRows map[int]bool
 	return m.renderTable(
-		[]string{"#", "NAME", "TYPE", "STATUS", "LATENCY", "UPTIME", "HISTORY", "SSL", "RETRY"},
+		[]string{"#", "NAME", "TYPE", "STATUS", "LAT", "UPTIME", "HISTORY", "SSL", "RETRY"},
 		len(m.sites),
 		func(start, end int) [][]string {
 			groupRows = make(map[int]bool)
@@ -764,6 +764,10 @@ func (m Model) viewDetailPanel() string {
 		fmt.Fprintf(&b, "  %-16s %s\n", subtleStyle.Render(label), value)
 	}
 
+	section := func(label string) {
+		b.WriteString("\n" + subtleStyle.Render("  "+label) + "\n")
+	}
+
 	row("Status", fmtStatus(site.Status, site.Paused, m.isMonitorInMaintenance(site.ID)))
 
 	if (site.Status == "DOWN" || site.Status == "SSL EXP" || site.Status == "LATE") && site.LastError != "" {
@@ -792,6 +796,8 @@ func (m Model) viewDetailPanel() string {
 			}
 		}
 	}
+
+	section("ENDPOINT")
 	row("Type", site.Type)
 	if site.URL != "" {
 		row("URL", site.URL)
@@ -802,31 +808,45 @@ func (m Model) viewDetailPanel() string {
 	if site.Port > 0 {
 		row("Port", strconv.Itoa(site.Port))
 	}
+
+	section("TIMING")
 	row("Interval", fmt.Sprintf("%ds", site.Interval))
-	row("Timeout", fmt.Sprintf("%ds", site.Timeout))
+	if site.Timeout > 0 {
+		row("Timeout", fmt.Sprintf("%ds", site.Timeout))
+	}
 	row("Latency", fmtLatency(site.Latency))
 	row("Uptime", fmtUptime(hist.Statuses))
+	if !site.LastCheck.IsZero() {
+		row("Last Check", site.LastCheck.Format("15:04:05"))
+	}
 
 	if site.Type == "http" {
-		row("Method", site.Method)
-		row("Codes", site.AcceptedCodes)
+		section("HTTP")
+		if site.Method != "" && site.Method != "GET" {
+			row("Method", site.Method)
+		}
+		codes := site.AcceptedCodes
+		if codes == "" {
+			codes = "200-299"
+		}
+		row("Codes", codes)
 		row("SSL", fmtSSL(site))
 		if site.IgnoreTLS {
 			row("TLS Verify", dangerStyle.Render("disabled"))
 		}
 	}
 
-	if site.MaxRetries > 0 {
-		row("Retries", fmtRetries(site))
-	}
-	if site.Regions != "" {
-		row("Regions", site.Regions)
-	}
-	if site.Description != "" {
-		row("Description", site.Description)
-	}
-	if !site.LastCheck.IsZero() {
-		row("Last Check", site.LastCheck.Format("15:04:05"))
+	if site.MaxRetries > 0 || site.Regions != "" || site.Description != "" {
+		section("CONFIG")
+		if site.MaxRetries > 0 {
+			row("Retries", fmtRetries(site))
+		}
+		if site.Regions != "" {
+			row("Regions", site.Regions)
+		}
+		if site.Description != "" {
+			row("Description", site.Description)
+		}
 	}
 
 	probeResults := m.engine.GetProbeResults(site.ID)