feat(tui): response time distribution histogram in full-screen detail

Horizontal bar chart showing latency distribution across 5 buckets:
0-50ms, 50-100ms, 100-200ms, 200-500ms, 500ms+. Color-coded green
(fast), yellow (medium), red (slow). Shows count per bucket.

Appears in the full-screen detail panel (Enter) after the sparkline
stats. Skipped for push monitors (no latency data).

internal/tui/histogram.go

@@ -0,0 +1,89 @@
+package tui
+
+import (
+	"fmt"
+	"strings"
+	"time"
+
+	"github.com/charmbracelet/lipgloss"
+)
+
+type latencyBucket struct {
+	label string
+	min   int64
+	max   int64
+	count int
+}
+
+func (m Model) latencyHistogram(latencies []time.Duration, statuses []bool, width int) string {
+	if len(latencies) == 0 || width < 30 {
+		return ""
+	}
+
+	buckets := []latencyBucket{
+		{"0-50ms", 0, 50, 0},
+		{"50-100ms", 50, 100, 0},
+		{"100-200ms", 100, 200, 0},
+		{"200-500ms", 200, 500, 0},
+		{"500ms+", 500, 999999, 0},
+	}
+
+	for i, l := range latencies {
+		if i < len(statuses) && !statuses[i] {
+			continue
+		}
+		ms := l.Milliseconds()
+		for j := range buckets {
+			if ms >= buckets[j].min && ms < buckets[j].max {
+				buckets[j].count++
+				break
+			}
+		}
+	}
+
+	maxCount := 0
+	for _, b := range buckets {
+		if b.count > maxCount {
+			maxCount = b.count
+		}
+	}
+	if maxCount == 0 {
+		return ""
+	}
+
+	labelW := 10
+	countW := len(fmt.Sprintf("%d", maxCount))
+	barW := width - labelW - countW - 4
+	if barW < 5 {
+		barW = 5
+	}
+
+	var sb strings.Builder
+	for _, b := range buckets {
+		fill := 0
+		if maxCount > 0 {
+			fill = b.count * barW / maxCount
+		}
+
+		var barColor lipgloss.Style
+		switch {
+		case b.min < 100:
+			barColor = m.st.specialStyle
+		case b.min < 500:
+			barColor = m.st.warnStyle
+		default:
+			barColor = m.st.dangerStyle
+		}
+
+		bar := barColor.Render(strings.Repeat("█", fill))
+		if fill < barW {
+			bar += m.st.subtleStyle.Render(strings.Repeat("░", barW-fill))
+		}
+
+		label := fmt.Sprintf("%*s", labelW, b.label)
+		count := fmt.Sprintf("%*d", countW, b.count)
+		sb.WriteString("  " + m.st.subtleStyle.Render(label) + " " + bar + " " + count + "\n")
+	}
+
+	return sb.String()
+}

internal/tui/view_detail.go

@@ -258,6 +258,15 @@ func (m Model) viewDetailPanel() string {
 		b.WriteString("\n" + m.renderSparkTooltip(site, hist, detailSparkWidth))
 	}
 
+	if site.Type != "push" && len(hist.Latencies) > 5 {
+		histW := m.termWidth - chromePadH - 4
+		if histW < 30 {
+			histW = 30
+		}
+		b.WriteString("\n\n" + m.st.subtleStyle.Render("  RESPONSE TIME DISTRIBUTION") + "\n")
+		b.WriteString(m.latencyHistogram(hist.Latencies, hist.Statuses, histW))
+	}
+
 	b.WriteString("\n")
 	b.WriteString(m.divider() + "\n")
 	b.WriteString(m.st.subtleStyle.Render("  [q/Esc] Back  [e] Edit  [h] History  [s] SLA  [click] Inspect"))